Method for isolating cells expressing FLk-2 receptors and isolated populations of cells that express FLk-2 receptors

ABSTRACT

Isolated mammalian nucleic acid molecules encoding receptor protein tyrosine kinases expressed in primitive hematopoietic cells and not expressed in mature hematopoietic cells are provided. Also included are the receptors encoded by such nucleic acid molecules; the nucleic acid molecules encoding receptor protein tyrosine kinases having the sequences shown in FIG.  1   a  (murine flk-2), FIG.1 b  (human flk-2) and FIG.  2  (murine flk-1); the receptor protein tyrosine kinases having the amino acid sequences shown in FIG.  1   a , FIG.  1   b  and FIG.  2;  ligands for the receptors; nucleic acid sequences that encode the ligands; and methods of stimulating the proliferation and/or differentiation of primitive mammalian hematopoietic stem cells comprising contacting the stem cells with a ligand that binds to a receptor protein tyrosine kinase expressed in primitive mammalian hematopoietic cells and not expressed in mature hematopoietic cells.

[0001] This application is a continuation-in-part of unassigned serial number filed Nov. 12, 1992, which is a continuation-in-part of Ser. No. 906,397 filed Jun. 26, 1992, which is is a continuation-in-part of Ser. No. 813,593 filed Dec. 24, 1991, which is a continuation-in-part of Ser. No. 793,065 filed Nov. 15, 1991, which is a continuation-in-part of Ser. No. 728,913 filed Jun. 28, 1991, which is a continuation-in-part of Ser. No. 679,666 filed Apr. 2, 1991, all of which are incorporated herein by reference.

[0002] The invention described in this application was made with U.S. government support from Grant Numbers R01-CA45339 and R01-DK42989 awarded by the National Institutes of Health. The government has certain rights in this invention.

FIELD OF THE INVENTION

[0003] The present invention relates to hematopoietic stem cell receptors, ligands for such receptors, and nucleic acid molecules encoding such receptors and ligands.

BACKGROUND OF THE INVENTION

[0004] The mammalian hematopoietic system comprises red and white blood cells. These cells are the mature cells that result from more primitive lineage-restricted cells. The cells of the hematopoietic system have been reviewed by Dexter and Spooncer in the Annual Review of Cell Biology 3, 423-441 (1987).

[0005] The red blood cells, or erythrocytes, result from primitive cells referred to by Dexter and Spooncer as erythroid burst-forming units (BFU-E) . The immediate progeny of the erythroid burst-forming units are called erythroid colony-forming units (CFU-E).

[0006] The white blood cells contain the mature cells of the lymphoid and myeloid systems. The lymphoid cells include B lymphocytes and T lymphocytes. The B and T lymphocytes result from earlier progenitor cells referred to by Dexter and Spooncer as preT and preB cells.

[0007] The myeloid system comprises a number of cells including granulocytes, platelets, monocytes, macrophages, and megakaryocytes. The granulocytes are further divided into neutrophils, ecsinophils, basophils and mast cells.

[0008] Each of the mature hematopoietic cells are specialized for specific functions. For example, erythrocytes are responsible for oxygen and carbon dioxide transport. T and B lymphocytes are responsible for cell-and antibody-mediated immune responses, respectively. Platelets are involved in blood clotting. Granulocytes and macrophages act generally as scavengers and accessory cells in the immune response against invading organisms and their by-products.

[0009] At the center of the hematopoietic system lie one or more totipotent hematopoietic stem cells, which undergo a series of differentiation steps leading to increasingly lineage-restricted progenitor cells. The more mature progenitor cells are restricted to producing one or two lineages. Some examples of lineage-restricted progenitor cells mentioned by Dexter and Spooncer include granulocyte/macrophage colony-forming cells (GM-CFC), megakaryocyte colony-forming cells (Meg-CFC), eosinophil colony-forming cells (Eos-CFC), and basophil colony-forming cells (Bas-CFC). Other examples of progenitor cells are discussed above.

[0010] The hematopoietic system functions by means of a precisely controlled production of the various mature lineages. The totipotent stem cell possesses the ability both to self renew and to differentiate into committed progenitors for all hematopoietic lineages. These most primitive of hematopoietic cells are both necessary and sufficient for the complete and permanent hematopoietic reconstitution of a radiation-ablated hematopoietic system in mammals. The ability of stem cells to reconstitute the entire hematopoietic system is the basis of bone marrow transplant therapy.

[0011] It is known that growth factors play an important role in the development and operation of the mammalian hematopoietic system. The role of growth factors is complex, however, and not well understood at the present time. One reason for the uncertainty is that much of what is known about hematopoietic growth factors results from in vitro experiments. Such experiments do not necessarily reflect in vivo realities.

[0012] In addition, in vitro hematopoiesis can be established in the absence of added growth factors, provided that marrow stromal cells are added to the medium. The relationship between stromal cells and hematopoietic growth factors in vivo is not understood. Nevertheless, hematopoietic growth factors have been shown to be highly active in vivo.

[0013] From what is known about them, hematopoietic growth factors appear to exhibit a spectrum of activities. At one end of the spectrum are growth factors such as erythropoietin, which is believed to promote proliferation only of mature erythroid progenitor cells. In the middle of the spectrum are growth factors such as IL-3, which is believed to facilitate the growth and development of early stem cells as well as of numerous progenitor cells. Some examples of progenitor cells induced by IL-3 include those restricted to the granulocyte/macrophage, eosinophil, megakaryocyte, erythroid and mast cell lineages.

[0014] At the other end of the spectrum is the hematopoietic growth factor that, along with the corresponding receptor, was discussed in a series of articles in the Oct. 5, 1990 edition of Cell. The receptor is the product of the W locus, c-kit, which is a member of the class of receptor protein tyrosine kinases. The ligand for c-kit, which is referred to by various names such as stem cell factor (SCF) and mast cell growth factor (MGF), is believed to be essential for the development of early hematopoietic stem cells and cells restricted to the erythroid and mast cell lineages in mice; see, for example, Copeland et al., Cell 63, 175-183 (1990).

[0015] It appears, therefore, that there are growth factors that exclusively affect mature cells. There also appear to be growth factors that affect both mature cells and stem cells. The growth factors that affect both types of cells may affect a small number or a large number of mature cells.

[0016] There further appears to be an inverse relationship between the ability of a growth factor to affect mature cells and the ability of the growth factor to affect stem cells. For example, the c-kit ligand, which stimulates a small number of mature cells, is believed to be more important in the renewal and development of stem cells then is IL-3, which is reporter to stimulate proliferation of many mature cells (see above).

[0017] Prior to the present specification, there have been no reports of growth factors that exclusively stimulate stem cells in the absence of an effect on mature cells. The discovery of such growth factors would be of particular significance.

[0018] As mentioned above, c-kit is a protein tyrosine kinase (pTK). It is becoming increasingly apparent that the protein tyrosine kinases play an important role as cellular receptors for hematopoietic growth factors. Other receptor pTKs include the receptors of colony stimulating factor 1 (CSF-1) and PDGF.

[0019] The pTK family can be recognized by the presence of several conserved amino acid regions in the catalytic domain. These conserved regions are summarized by Hanks et al. in Science 241, 42-52 (1988), see FIG. 1 starting on page 46 and by Wilks in Proc. Natl. Acad. Sci. USA 86, 1603-1607 (1989), see FIG. 2 on page 1605.

[0020] Additional protein tyrosine kinases that represent hematopoietic growth factor receptors are needed in order more effectively to stimulate the self-renewal of the totipotent hematopoietic stem cell and to stimulate the development of all cells of the hematopoietic system both in vitro and in vivo. Novel hematopoietic growth factor receptors that are present only on primitive stem cells, but are not present on mature progenitor cells, are particularly desired. Ligands for the novel receptors are also desirable to act as hematopoietic growth factors. Nucleic acid sequences encoding the receptors and ligands are needed to produce recombinant receptors and ligands.

SUMMARY OF THE INVENTION

[0021] These and other objectives as will be apparent to those with ordinary skill in the art have been met by providing isolated mammalian nucleic acid molecules encoding receptor protein tyrosine kinases expressed in primitive hematopoietic cells and not expressed in mature hematopoietic cells. Also included are the receptors encoded by such nucleic acid molecules; the nucleic acid molecules encoding receptor protein tyrosine kinases having the sequences shown in FIG.1a (murine flk-2), FIG.1b (human flk-2) and FIG. 2 (murine flk-1); the receptor protein tyrosine kinases having the amino acid sequences shown in FIG.1a, FIG.1b and FIG. 2; ligands for the receptors; nucleic acid sequences that encode the ligands; and methods of stimulating the proliferation of primitive mammalian hematopoietic stem cells comprising contacting the stem cells with a ligand that binds to a receptor protein tyrosine kinase expressed in primitive mammalian hematopoietic cells and not expressed in mature hematopoietic cells.

DESCRIPTION OF THE FIGURES

[0022]FIGS. 1a.1 through 1 a.6 shows the cDNA and amino acid sequences of murine flk-2. All subsequent references to FIG. 1a are intended to refer to FIGS. 1a.1 through 1 a.6. The amino acid residues occur directly below the nucleotides in the open reading frame. Amino acids −27 to −1 constitute the hydrophobic leader sequence. Amino acids 1 to 517 constitute the extracellular receptor domain. Amino acids 518 to 537 constitute the transmembrane region. Amino acids 538 to 966 constitute the intracellular catalytic domain. Counting amino acid residue −27 as residue number 1, the following amino acid residues in the intracellular domain are catalytic sub-domains identified by Hanks (see above): 618-623, 811-819, 832-834, 857-862, 872-878 The sequence at residues 709-785 is a signature sequence characteristic of flk-2. The protein tyrosine kinases generally have a signature sequence in this region. (See SEQ. ID. NOS. 1-2)

[0023]FIGS. 1b.1 through 1 b.6 shows the complete cDNA and amino acid sequences of human flk-2 receptor. All subsequent references to FIG. 1b are intended to refer to FIGS. 1b.1 through 1 b.6. Amino acids −27 to −1 constitute the hydrophobic leader sequence. Amino acids 1 to 516 constitute the extracellular receptor domain. Amino acids 517 to 536 constitute the transmembrane region. Amino acids 537 to 966 constitute the intracellular catalytic domain. (See SEQ. ID. NOS. 3-4)

[0024]FIGS. 2.1 through 2.9 shows the cDNA and amino acid sequences of murine flk-1. All subsequent references to FIG. 2 are intended to refer to FIGS. 2.1 through 2.9. Amino acids −19 to −1 constitute the hydrophobic leader sequence. Amino acids 1 to 743 constitute the extracellular receptor domain. Amino acids 744 to 765 constitute the transmembrane region. Amino acids 766 to 1348 constitute the intracellular catalytic domain. (See SEQ. ID. NOS. 5-6)

[0025]FIG. 3 shows the time response of binding between a murine stromal cell line (2018) and APtag-flk-2 as well as APtag-flk-1. APtag without receptor (SEAP) is used as a control. See Example 8.

[0026]FIG. 4 shows the dose response of binding between stromal cells (2018) and APtag-flk-2 as well as APtag-flk-1. APtag without receptor (SEAP) is used as a control. See Example 8.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Receptors

[0028] In one embodiment, the invention relates to an isolated mammalian nucleic acid molecule encoding a receptor protein tyrosine kinase expressed in primitive mammalian hematopoietic cells and not expressed in mature hematopoietic cells.

[0029] The nucleic acid molecule may be a DNA, cDNA, or RNA molecule. The mammal in which the nucleic acid molecule exists may be any mammal, such as a mouse, rat, rabbit, or human.

[0030] The nucleic acid molecule encodes a protein tyrosine kinase (pTK). Members of the pTK family can be recognized by the conserved amino acid regions in the catalytic domains. Examples of pTK consensus sequences have been provided by Hanks et al. in Science 241, 42-52 (1988); see especially FIG. 1 starting on page 46 and by Wilks in Proc. Natl. Acad. Sci. USA 86, 1603-1607 (1989); see especially FIG. 2 on page 1605. A methionine residue at position 205 in the conserved sequence WMAPES is characteristic of pTK's that are receptors.

[0031] The Hanks et al article identifies eleven catalytic sub-domains containing pTK consensus residues and sequences. The pTKs of the present invention will have most or all of these consensus residues and sequences.

[0032] Some particularly strongly conserved residues and sequences are shown in Table 1. TABLE 1 Conserved Residues and Sequences in pTKs¹ Residue or Catalytic Position² Sequence Domain  50 G I  52 G I  57 V I  70 A II  72 K II  91 E III 166 D VI 171 N VI 184-186 DFG VII 208 E VIII 220 D IX 225 G IX 280 R XI

[0033] A pTK of the invention may contain all thirteen of these highly conserved residues and sequences. As a result of natural or synthetic mutations, the pTKs of the invention may contain fewer than all thirteen strongly conserved residues and sequences, such as 11, 9, or 7 such sequences.

[0034] The receptors of the invention generally belong to the same class of pTK sequences that c-kit belongs to. It has surprisingly been discovered, however, that a new functional class of receptor pTKs exists. The new functional class of receptor pTKs is expressed in primitive hematopoietic cells, but not expressed in mature hematopoietic cells.

[0035] For the purpose of this specification, a primitive hematopoietic cell is totipotent, i.e. capable of reconstituting all hematopoietic blood cells in vivo. A mature hematopoietic cell is non-self-renewing, and has limited proliferative capacity—i.e., a limited ability to give rise to multiple lineages. Mature hematopoietic cells, for the purposes of this specification, are generally capable of giving rise to only one or two lineages in vitro or in vivo.

[0036] It should be understood that the hematopoietic system is complex, and contains many intermediate cells between the primitive totipotent hematopoietic stem cell and the totally committed mature hematopoietic cells defined above. As the stem cell develops into increasingly mature, lineage-restricted cells, it gradually loses its capacity for self-renewal.

[0037] The receptors of the present invention may and may not be expressed in these intermediate cells. The necessary and sufficient condition that defines members of the new class of receptors is that they are present in the primitive, totipotent stem cell or cells, and not in mature cells restricted only to one or, at most, two lineages.

[0038] An example of a member of the new class of receptor pTKs is called fetal liver kinase 2 (flk-2) after the organ in which it was found. There is approximately 1 totipotent stem cell per 10⁴ cells in mid-gestation (day 14) fetal liver in mice. In addition to fetal liver, flk-2 is also expressed in fetal spleen, fetal thymus, adult brain, and adult marrow.

[0039] For example, flk-2 is expressed in individual multipotential CFU-Blast colonies capable of generating numerous multilineage colonies upon replating. It is likely, therefore, that flk-2 is expressed in the entire primitive (i.e. self-renewing) portion of the hematopoietic hierarchy. This discovery is consistent with flk-2 being important in transducing putative self-renewal signals from the environment.

[0040] It is particularly relevant that the expression of flk-2 mRNA occurs in the most primitive thymocyte subset. Even in two closely linked immature subsets that differ in expression of the IL-2 receptor, flk-2 expression segregates to the more primitive subset lacking an IL-2 receptor. The earliest thymocyte subset is believed to be uncommitted. Therefore, the thymocytes expressing flk-2 may be multipotential. flk-2 is the first receptor tyrosine kinase known to be expressed in the T-lymphoid lineage.

[0041] The fetal liver mRNA migrates relative to 28S and 18S ribosomal bands on formaldehyde agarose gels at approximately 3.5 kb, while the brain message is considerably larger. In adult tissues, flk-2 m-RNA from both brain and bone marrow migrated at approximately 3.5 kb.

[0042] A second pTK receptor is also included in the present invention. This second receptor, which is called fetal liver kinase 1 (flk-1), is not a member of the same class of receptors as flk-2, since flk-1 may be found in some more mature hematopoietic cells. The amino acid sequence of murine flk-1 is given in FIG. 2.

[0043] The present invention includes the flk-1 receptor as well as DNA, cDNA and RNA encoding flk-1. The DNA sequence of murine flk-1 is also given in FIG. 2. Flk-1 may be found in the same organs as flk-2, as well as in fetal brain, stomach, kidney, lung, heart and intestine; and in adult kidney, heart, spleen, lung, muscle, and lymph nodes.

[0044] The receptor protein tyrosine kinases of the invention are known to be divided into easily found domains. The DNA sequence corresponding to the pTKs encode, starting at their 5′-ends, a hydrophobic leader sequence followed by a hydrophilic extracellular domain, which binds to, and is activated by, a specific ligand. Immediately downstream from the extracellular receptor domain, is a hydrophobic transmembrane region. The transmembrane region is immediately followed by a basic catalytic domain, which may easily be identified by reference to the Hanks et al. and Wilks articles discussed above.

[0045] The following table shows the nucleic acid and amino acid numbers that correspond to the signal peptide, the extracellular domain, the transmembrane region and the intracellular domain for murine flk-1 (mflk-1), murine flk-2 (mflk-2) and human flk-2 (hflk-2). Signal Peptide Extracellular Transmembrane Intracellular mFLK-1 aa # −19 to −1 1 to 743 744 to 765  766 to 1348 aa code M  A A  E V  V R  A na #  208-264 265-2493 2494-2559 2560-4308 mFLK-2 aa # −27 to −1 1 to 517 518 to 537 538 to 966 aa code M  T N  S F  C H  S na #  31-111 112-1662 1663-1722 1723-3006 hFLK-2 aa # −27 to −1 1 to 516 517 to 536 537 to 966 aa code M  N Q  F Y  C H  S na #  58-138 139-1689 1690-1746 1747-3036

[0046] The present invention includes the extracellular receptor domain lacking the transmembrane region and catalytic domain. Preferably, the hydrophobic leader sequence is also removed from the extracellular domain. In the case of human and murine flk-2, the hydrophobic leader sequence includes amino acids −27 to −1.

[0047] These regions and domains may easily be visually identified by those having ordinary skill in the art by reviewing the amino acid sequence in a suspected pTK and comparing it to known pTKs. For example, referring to FIG. 1a, the transmembrane region of flk-2, which separates the extracellular receptor domain from the catalytic domain, is encoded by nucleotides 1663 (T) to 1722 (C). These nucleotides correspond to amino acid residues 545 (Phe) to 564 (Cys). The amino acid sequence between the transmembrane region and the catalytic sub-domain (amino acids 618-623) identified by Hanks et al. as sub-domain I (i.e., GXGXXG) is characteristic of receptor protein tyrosine kinases.

[0048] The extracellular domain may also be identified through commonly recognized criteria of extracellular amino acid sequences. The determination of appropriate criteria is known to those skilled in the art, and has been described, for example, by Hopp et al, Proc. Nat'l Acad. Sci. USA 78, 3824-3828 (1981); Kyte et al, J. Mol. Biol. 157, 105-132 (1982); Emini, J. Virol. 55, 836-839 (1985); Jameson et al, CA BIOS 4, 181-186 (1988); and Karplus et al, Naturwissenschaften 72, 212-213 (1985). Amino acid domains predicted by these criteria to be surface exposed characteristic of extracellular domains.

[0049] As will be discussed in more detail below, the nucleic acid molecules that encode the receptors of the invention may be inserted into known vectors for use in standard recombinant DNA techniques. Standard recombinant DNA techniques are those such as are described in Sambrook et al., “Molecular Cloning,” Second Edition, Cold Spring Harbor Laboratory Press (1987) and by Ausubel et al., Eds, “Current Protocols in Molecular Biology,” Green Publishing Associates and Wiley-Interscience, New York (1987). The vectors may be circular (i.e. plasmids) or non-circular. Standard vectors are available for cloning and expression in a host. The host may be prokaryotic or eucaryotic. Prokaryotic hosts are preferably E. coli. Preferred eucaryotic hosts include yeast, insect and mammalian cells. Preferred mammalian cells include, for example, CHO, COS and human cells.

[0050] Ligands

[0051] The invention also includes ligands that bind to the receptor pTKs of the invention. In addition to binding, the ligands stimulate the proliferation of additional primitive stem cells, differentiation into more mature progenitor cells, or both.

[0052] The ligand may be a growth factor that occurs naturally in a mammal, preferably the same mammal that produces the corresponding receptor. The growth factor may be isolated and purified, or be present on the surface of an isolated population of cells, such as stromal cells.

[0053] The ligand may also be a molecule that does not occur naturally in a mammal. For example, antibodies, preferably monoclonal, raised against the receptors of the invention or against anti-ligand antibodies mimic the shape of, and act as, ligands if they constitute the negative image of the receptor or anti-ligand antibody binding site. The ligand may also be a non-protein molecule that acts as a ligand when it binds to, or otherwise comes into contact with, the receptor.

[0054] In another embodiment, nucleic acid molecules encoding the ligands of the invention are provided. The nucleic acid molecule may be RNA, DNA or cDNA.

[0055] Stimulating Proliferation of Stem Cells

[0056] The invention also includes a method of stimulating the proliferation and/or differentiation of primitive mammalian hematopoietic stem cells as defined above. The method comprises contacting the stem cells with a ligand in accordance with the present invention. The stimulation of proliferation and/or differentiation may occur in vitro or in vivo.

[0057] The ability of a ligand according to the invention to stimulate proliferation of stem cells in vitro and in vivo has important therapeutic applications. Such applications include treating mammals, including humans, whose primitive stem cells do not sufficiently undergo self-renewal. Example of such medical problems include those that occur when defects in hematopoietic stem cells or their related growth factors depress the number of white blood cells. Examples of such medical problems include anemia, such as macrocytic and aplastic anemia. Bone marrow damage resulting from cancer chemotherapy and radiation is another example of a medical problem that would be helped by the stem cell factors of the invention.

[0058] Functional Equivalents

[0059] The invention includes functional equivalents of the pTK receptors, receptor domains, and ligands described above as well as of the nucleic acid sequences encoding them. A protein is considered a functional equivalent of another protein for a specific function if the equivalent protein is immunologically cross-reactive with, and has the same function as, the receptors and ligands of the invention. The equivalent may, for example, be a fragment of the protein, or a substitution, addition or deletion mutant of the protein.

[0060] For example, it is possible to substitute amino acids in a sequence with equivalent amino acids. Groups of amino acids known normally to be equivalent are: (a)Ala(A) Ser(S) Thr(T) Pro(P) Gly(G); (b)Asn(N) Asp(D) Glu(E) Gln(Q); (c)His(N) Arg(R) Lys(K); (d)Met(M) Leu(L) Ile(I) Val(V); and (e)Phe(F) Tyr(Y) Trp(W).

[0061] Substitutions, additions and/or deletions in the receptors and ligands may be made as long as the resulting equivalent receptors and ligands are immunologically cross reactive with, and have the same function as, the native receptors and ligands.

[0062] The equivalent receptors and ligands will normally have substantially the same amino acid sequence as the native receptors and ligands. An amino acid sequence that is substantially the same as another sequence, but that differs from the other sequence by means of one or more substitutions, additions and/or deletions is considered to be an equivalent sequence. Preferably, less than 25%, more preferably less than 10%, and most preferably less than 5% of the number of amino acid residues in the amino acid sequence of the native receptors and ligands are substituted for, added to, or deleted from.

[0063] Equivalent nucleic acid molecules include nucleic acid sequences that encode equivalent receptors and ligands as defined above. Equivalent nucleic acid molecules also include nucleic acid sequences that differ from native nucleic acid sequences in ways that do not affect the corresponding amino acid sequences.

Isolation of Nucleic Acid Molecules and Proteins

[0064] Isolation of Nucleic Acid Molecules Encoding Receptors

[0065] In order to produce nucleic acid molecules encoding mammalian stem cell receptors, a source of stem cells is provided. Suitable sources include fetal liver, spleen, or thymus cells or adult marrow or brain cells.

[0066] For example, suitable mouse fetal liver cells may be obtained at day 14 of gestation. Mouse fetal thymus cells may be obtained at day 14-18, preferably day 15, of gestation. Suitable fetal cells of other mammals are obtained at gestation times corresponding to those of mouse.

[0067] Total RNA is prepared by standard procedures from stem cell receptor-containing tissue. The total RNA is used to direct cDNA synthesis. Standard methods for isolating RNA and synthesizing cDNA are provided in standard manuals of molecular biology such as, for example, in Sambrook et al., “Molecular Cloning,” Second Edition, Cold Spring Harbor Laboratory Press (1987) and in Ausubel et al., (Eds), “Current Protocols in Molecular Biology,” Greene Associates/Wiley Interscience, New York (1990).

[0068] The cDNA of the receptors is amplified by known methods. For example, the cDNA may be used as a template for amplification by polymerase chain reaction (PCR); see Saiki et al., Science, 239, 487 (1988) or Mullis et al., U.S. Pat. No. 4,683,195. The sequences of the oligonucleotide primers for the PCR amplification are derived from the sequences of known receptors, such as from the sequences given in FIGS. 1 and 2 for flk-2 and flk-1, respectively, preferably from flk-2. The oligonucleotides are synthesized by methods known in the art. Suitable methods include those described by Caruthers in Science 230, 281-285 (1985).

[0069] In order to isolate the entire protein-coding regions for the receptors of the invention, the upstream oligonucleotide is complementary to the sequence at the 5′ end, preferably encompassing the ATG start codon and at least 5-10 nucleotides upstream of the start codon. The downstream oligonucleotide is complementary to the sequence at the 3′ end, optionally encompassing the stop codon. A mixture of upstream and downstream oligonucleotides are used in the PCR amplification. The conditions are optimized for each particular primer pair according to standard procedures. The PCR product is analyzed by electrophoresis for the correct size cDNA corresponding to the sequence between the primers.

[0070] Alternatively, the coding region may be amplified in two or more overlapping fragments. The overlapping fragments are designed to include a restriction site permitting the assembly of the intact cDNA from the fragments.

[0071] The amplified DNA encoding the receptors of the invention may be replicated in a wide variety of cloning vectors in a wide variety of host cells. The host cell may be prokaryotic or eukaryotic. The DNA may be obtained from natural sources and, optionally, modified, or may be synthesized in whole or in part.

[0072] The vector into which the DNA is spliced may comprise segments of chromosomal, non-chromosomal and synthetic DNA sequences. Some suitable prokaryotic cloning vectors include plasmids from E. coli, such as colE1, pCR1, pBR322, pMB9, pUC, pKSM, and RP4. Prokaryotic vectors also include derivatives of phage DNA such as M13 and other filamentous single-stranded DNA phages.

[0073] Isolation of Receptors

[0074] DNA encoding the receptors of the invention are inserted into a suitable vector and expressed in a suitable prokaryotic or eucaryotic host. Vectors for expressing proteins in bacteria, especially E. coli, are known. Such vectors include the PATH vectors described by Dieckmann and Tzagoloff in J. Biol. Chem. 260, 1513-1520 (1985). These vectors contain DNA sequences that encode anthranilate synthetase (TrpE) followed by a polylinker at the carboxy terminus. Other expression vector systems are based on beta-galactosidase (pEX); lambda P_(L); maltose binding protein (pMAL); and glutathione S-transferase (pGST)—see Gene 67, 31 (1988) and Peptide Research 3, 167 (1990).

[0075] Vectors useful in yeast are available. A suitable example is the 2μ plasmid.

[0076] Suitable vectors for use in mammalian cells are also known. Such vectors include well-known derivatives of SV-40, adenovirus, retrovirus-derived DNA sequences and shuttle vectors derived from combination of functional mammalian vectors, such as those described above, and functional plasmids and phage DNA.

[0077] Further eukaryotic expression vectors are known in the art (e.g., P. J. Southern and P. Berg, J. Mol. Appl. Genet. 1, 327-341 (1982); S. Subramani et al, Mol. Cell. Biol. 1, 854-864 (1981); R. J. Kaufmann and P. A. Sharp, “Amplification And Expression Of Sequences Cotransfected with A Modular Dihydrofolate Reductase Complementary DNA Gene,” J. Mol. Biol. 159, 601-621 (1982); R. J. Kaufmann and P. A. Sharp, Mol. Cell. Biol. 159, 601-664 (1982); S. I. Scahill et al, “Expression And Characterization Of The Product Of A Human Immune Interferon DNA Gene In Chinese Hamster Ovary Cells,” Proc. Natl. Acad. Sci. USA 80, 4654-4659 (1983); G. Urlaub and L. A. Chasin, Proc. Natl. Acad. Sci. USA 77, 4216-4220, (1980).

[0078] The expression vectors useful in the present invention contain at least one expression control sequence that is operatively linked to the DNA sequence or fragment to be expressed. The control sequence is inserted in the vector in order to control and to regulate the expression of the cloned DNA sequence. Examples of useful expression control sequences are the lac system, the trp system, the tac system, the trc system, major operator and promoter regions of phage lambda, the control region of fd coat protein, the glycolytic promoters of yeast, e.g., the promoter for 3-phosphoglycerate kinase, the promoters of yeast acid phosphatase, e.g., Pho5, the promoters of the yeast alpha-mating factors, and promoters derived from polyoma, acenovirus, retrovirus, and simian virus, e.g., the early and late promoters or SV40, and other sequences known to control the expression of genes of prokaryotic or eukaryotic cells and their viruses or combinations thereof.

[0079] Vectors containing the receptor-encoding DNA and control signals are inserted into a host cell for expression of the receptor. Some useful expression host cells include well-known prokaryotic and eukaryotic cells. Some suitable prokaryotic hosts include, for example, E. coli, such as E. coli SG-936, E. coli HB 101, E. coli W3110, E. coli X1776, E. coli X2282, E. coli DHI, and E. coli MRC1, Pseudomonas, Bacillus, such as Bacillus subtilis, and Streptomyces. Suitable eukaryotic cells include yeast and other fungi, insect, animal cells, such as COS cells and CHO cells, human cells and plant cells in tissue culture.

[0080] The human homologs of the mouse receptors described above are isolated by a similar strategy. RNA encoding the receptors are obtained from a source of human cells enriched for primitive stem cells. Suitable human cells include fecal spleen, thymus and liver cells, and umbilical cord blood as well as adult brain and bone marrow cells. The human fetal cells are preferably obtained on the day of gestation corresponding to mid-gestation in mice. The amino acid sequences of the human flk receptors as well as of the nucleic acid sequences encoding them are homologous to the amino acid and nucleotide sequences of the mouse receptors.

[0081] In the present specification, the sequence of a first protein, such as a receptor or a ligand, or of a nucleic acid molecule that encodes the protein, is considered homologous to a second protein or nucleic acid molecule if the amino acid or nucleotide sequence of the first protein or nucleic acid molecule is at least about 30% homologous, preferably at least about 50% homologous, and more preferably at least about 65% homologous to the respective sequences of the second protein or nucleic acid molecule. In the case of proteins having high homology, the amino acid or nucleotide sequence of the first protein or nucleic acid molecule is at least about 75% homologous, preferably at least about 85% homologous, and more preferably at least about 95% homologous to the amino acid or nucleotide sequence of the second protein or nucleic acid molecule.

[0082] Combinations of mouse oligonucleotide pairs are used as PCR primers to amplify the human homologs from the cells to account for sequence divergence. The remainder of the procedure for obtaining the human flk homologs are similar to those described above for obtaining mouse flk receptors. The less than perfect homology between the human flk homologs and the mouse oligonucleotides is taken into account in determining the stringency of the hybridization conditions.

[0083] Assay for expression of Receptors on Stem Cells

[0084] In order to demonstrate the expression of flk receptors on the surface of primitive hematopoietic stem cells, antibodies that recognize the receptor are raised. The receptor may be the entire protein as it exists in nature, or an antigenic fragment of the whole protein. Preferably, the fragment comprises the predicted extra-cellular portion of the molecule.

[0085] Antigenic fragments may be identified by methods known in the art. Fragments containing antigenic sequences may be selected on the basis of generally accepted criteria of potential antigenicity and/or exposure. Such criteria include the hydrophilicity and relative antigenic index, as determined by surface exposure analysis of proteins. The determination of appropriate criteria is known to those skilled in the art, and has been described, for example, by Hopp et al, Proc. Nat'l Acad. Sci. USA 78, 3824-3828 (1981); Kyte et al, J. Mol. Biol. 157, 105-132 (1982); Emini, J. Virol. 55, 836-839 (1985); Jameson et al, CA BIOS 4, 181-186 (1988); and Karplus et al, Naturwissenschaften 72, 212-213 (1985). Amino acid domains predicted by these criteria to be surface exposed are selected preferentially over domains predicted to be more hydrophobic or hidden.

[0086] The proteins and fragments of the receptors to be used as antigens may be prepared by methods known in the art. Such methods include isolating or synthesizing DNA encoding the proteins and fragments, and using the DNA to produce recombinant proteins, as described above.

[0087] Fragments of proteins and DNA encoding the fragments may be chemically synthesized by methods known in the art from individual amino acids and nucleotides. Suitable methods for synthesizing protein fragments are described by Stuart and Young in “Solid Phase Peptide Synthesis,” Second Edition, Pierce Chemical Company (1984). Suitable methods for synthesizing DNA fragments are described by Caruthers in Science 230, 281-285 (1985).

[0088] If the receptor fragment defines the epitope, but is too short to be antigenic, it may be conjugated to a carrier molecule in order to produce antibodies. Some suitable carrier molecules include keyhole limpet hemocyanin, Ig sequences, TrpE, and human or bovine serum albumen. Conjugation may be carried out by methods known in the art. One such method is to combine a cysteine residue of the fragment with a cysteine residue on the carrier molecule.

[0089] The antibodies are preferably monoclonal. Monoclonal antibodies may be produced by methods known in the art. These methods include the immunological method described by Kohler and Milstein in Nature 256, 495-497 (1975) and Campbell in “Monoclonal Antibody Technology, The Production and Characterization Of Rodent and Human Hybridomas” in Burdon et al., Eds, Laboratory Techniques in Biochemistry and Molecular Biology, Volume 13, Elsevier Science Publishers, Amsterdam (1985); as well as by the recombinant DNA method described by Huse et al in Science 246, 1275-1281 (1989).

[0090] Polyclonal or monoclonal antisera shown to be reactive with receptor-encoded native proteins, such as with flk-1 and flk-2 encoded proteins, expressed on the surface of viable cells are used to isolate antibody-positive cells. One method for isolating such cells is flow cytometry; see, for example, Loken et al., European patent application 317,156. The cells obtained are assayed for stem cells by engraftment into radiation-ablated hosts by methods known in the art; see, for example, Jordan et al., Cell 61, 953-963 (1990).

[0091] Criteria for Novel Stem Cell Receptor Tyrosine Kinases Expressed in Stem Cells

[0092] Additional novel receptor tyrosine kinase cDNAs are obtained by amplifying cDNAs from stem cell populations using oligonucleotides as PCR primers; see above. Examples of suitable oligonucleotides are PTK1 and PTK2, which were described by Wilks et al. in Proc. Natl. Acad. Sci. USA 86, 1603-1607 (1989). Novel cDNA is selected on the basis of differential hybridization screening with probes representing known kinases. The cDNA clones hybridizing only at low stringency are selected and sequenced. The presence of the amino acid triplet DFG confirms that the sequence represents a kinase. The diagnostic methionine residue in the WMAPES motif is indicative of a receptor-like kinase, as described above. Potentially novel sequences obtained are compared to available sequences using databases such as Genbank in order to confirm uniqueness. Gene-specific oligonucleotides are prepared as described above based on the sequence obtained. The oligonucleotides are used to analyze stem cell enriched and depleted populations for expression. Such cell populations in mice are described, for example, by Jordan et al. in Cell 61, 953-956 (1990); Ikuta et al. in Cell 62, 863-864 (1990); Spangrude et al. in Science 241, 58-62 (1988); and Szilvassy et al. in Blood 74, 930-939 (1989). Examples of such human cell populations are described as CD33⁻CD34⁻ by Andrews et al. in the Journal of Experimental Medicine 169, 1721-1731 (1989). Other human stem cell populations are described, for example, in Civin et al., European Patent Application 395,355 and in Loken et al., European Patent Application 317,156.

[0093] Isolating Ligands and Nucleic Acid Molecules Encoding Ligands

[0094] Cells that may be used for obtaining ligands include stromal cells, for example stromal cells from fetal liver, fetal spleen, fetal thymus and fetal or adult bone marrow. Cell lines expressing ligands are established and screened.

[0095] For example, cells such as stromal (non-hematopoietic) cells from fetal liver are immortalized by known methods. Examples of known methods of immortalizing cells include transduction with a temperature sensitive SV40 T-antigen expressed in a retroviral vector. Infection of fetal liver cells with this virus permits the rapid and efficient establishment of multiple independent cell lines. These lines are screened for ligand activity by methods known in the art, such as those outlined below.

[0096] Ligands for the receptors of the invention, such as flk-1 and flk-2, may be obtained from the cells in several ways. For example, a bioassay system for ligand activity employs chimeric tagged receptors; see, for example, Flanagan et al., Cell 63, 185-194 (1990). One strategy measures ligand binding directly via a histochemical assay. Fusion proteins comprising the extracellular receptor domains and secretable alkaline phosphatase (SEAP) are constructed and transfected into suitable cells such as NIH/3T3 or COS cells. Flanagan et al refer to such DNA or amino acid constructs as APtag followed by the name of the receptor—i.e. APtag-c-kit. The fusion proteins bind with high affinity to cells expressing surface-bound ligand. Binding is detectable by the enzymatic activity of the alkaline phosphatase secreted into the medium. The bound cells, which are often stromal cells, are isolated from the APtag-receptor complex.

[0097] For example, some stromal cells that bind APtag-flk1 and APtag-flk2 fusion proteins include mouse fetal liver cells (see example 1); human fetal spleen cells (see example 3); and human fetal liver (example 3). Some stromal fetal thymus cells contain flk-1 ligand (example 3).

[0098] To clone the cDNA that encodes the ligand, a cDNA library is constructed from the isolated stromal cells in a suitable expression vector, preferably a phage such as CDM8, pSV Sport (BRL Gibco) or piH3, (Seed et al., Proc. Natl. Acad. Sci. USA 84, 3365-3369 (1987)). The library is transfected into suitable host cells, such as COS cells. Cells containing ligands on their surface are detected by known methods, see above.

[0099] In one such method, transfected COS cells are distributed into single cell suspensions and incubated with the secreted alkaline phosphatase-flk receptor fusion protein, which is present in the medium from NIH/3T3 or COS cells prepared by the method described by Flanagan et al., see above. Alkaline phosphatase-receptor fusion proteins that are not bound to the cells are removed by centrifugation, and the cells are panned on plates coated with antibodies to alkaline phosphatase. Bound cells are isolated following several washes with a suitable wash reagent, such as 5% fetal bovine serum in PBS, and the DNA is extracted from the cells. Additional details of the panning method described above may be found in an article by Seed et al., Proc. Natl. Acad. Sci. USA 84, 3365-3369 (1987).

[0100] In a second strategy, the putative extracellular ligand binding domains of the receptors are fused to the transmembrane and kinase domains of the human c-fms tyrosine kinase and introduced into 3T3 fibroblasts. The human c-fms kinase is necessary and sufficient to transduce proliferative signals in these cells after appropriate activation i.e. with the flk-1 or flk-2 ligand. The 3T3 cells expressing the chimeras are used to screen putative sources of ligand in a cell proliferation assay.

[0101] An alternate approach for isolating ligands using the fusion receptor-expressing 3T3 cells and insertional activation is also possible. A retrovirus is introduced into random chromosomal positions in a large population of these cells. In a small fraction, the retrovirus is inserted in the vicinity of the ligand-encoding gene, thereby activating it. These cells proliferate due to autocrine stimulation of the receptor. The ligand gene is “tagged” by the retrovirus, thus facilitating its isolation.

Examples Example 1 Cells Containing Mouse flk-1 and flk-2 Ligands

[0102] Murine stromal cell line 2018.

[0103] In order to establish stromal cell lines, fetal liver cells are disaggregated with collagen and grown in a mixture of Dulbecco's Modified Eagle's Medium (DMEM) and 10% heat-inactivated fetal calf serum at 37° C. The cells are immortalized by standard methods. A suitable method involves introducing DNA encoding a growth regulating- or oncogene-encoding sequence into the target host cell. The DNA may be introduced by means of transduction in a recombinant viral particle or transfection in a plasmid. See, for example, Hammerschmidt et al., Nature 340, 393-397 (1989) and Abcouwer et al, Biotechnology 7, 939-946 (1989). Retroviruses are the preferred viral vectors, although SV40 and Epstein-Barr virus can also serve as donors of the growth-enhancing sequences. A suitable retrovirus is the ecotropic retrovirus containing a temperature sensitive SV40 T-antigen (tsA58) and a G418 resistance gene described by McKay in Cell 66, 713-729 (1991). After several days at 37° C., the temperature of the medium is lowered to 32° C. Cells are selected with G418 (0.5 mg/ml). The selected cells are expanded and maintained.

[0104] A mouse stromal cell line produced by this procedure is called 2018 and was deposited on Oct. 30, 1991 in the American Type Culture Collection, Rockville, Md., USA (ATCC); accession number CRL 10907.

Example 2 Cells Containing Human flk-1 and flk-2 Ligands

[0105] Human fetal liver (18, 20, and 33 weeks after abortion), spleen (18 weeks after abortion), or thymus (20 weeks after abortion) is removed at the time of abortion and stored on ice in a balanced salt solution. After mincing into 1 mm fragments and forcing through a wire mesh, the tissue is washed one time in Hanks Balanced Salt Solution (HBSS).

[0106] The disrupted tissue is centrifuged at 200×g for 15 minutes at room temperature. The resulting pellet is resuspended in 10-20 ml of a tissue culture grade trypsin-EDTA solution (Flow Laboratories). The resuspended tissue is transferred to a sterile flask and stirred with a stirring bar at room temperature for 10 minutes. One ml of heat-inactivated fetal bovine calf serum (Hyclone) is added to a final concentration of 10% in order to inhibit trypsin activity. Collagenase type IV (Sigma) is added from a stock solution (10 mg/ml in HBSS) to a final concentration of 100 ug/ml in order to disrupt the stromal cells. The tissue is stirred at room temperature for an additional 2.5 hours; collected by centrifugation (400×g, 15 minutes); and resuspended in “stromal medium,” which contains Iscove's modification of DMEM supplemented with 10% heat-inactivated fetal calf serum, 5% heat-inactivated human serum (Sigma), 4 mM L-glutamine, 1×sodium pyruvate, (stock of 100×Sigma), 1×non-essential amino acids (stock of 100×, Flow), and a mixture of antibiotics kanomycin, neomycin, penicillin, streptomycin. Prior to resuspending the pellet in the stromal medium, the pellet is washed one time with HBSS. It is convenient to suspend the cells in 60 ml of medium. The number of cultures depends on the amount of tissue.

Example 3 Isolating Stromal cells

[0107] Resuspended Cells (example 2) that are incubated at 37° C. with 5% carbon dioxide begin to adhere to the plastic plate within 10-48 hours. Confluent monolayers may be observed within 7-10 days, depending upon the number of cells plated in the initial innoculum. Non-adherent and highly refractile cells adhering to the stromal cell layer as colonies are separately removed by pipetting and frozen. Non-adherent cells are likely sources of populations of self-renewing stem cells containing flk-2. The adherent stromal cell layers are frozen in aliquots for future studies or expanded for growth in culture.

[0108] An unexpectedly high level of APtag-flk-2 fusion protein binding to the fetal spleen cells is observed. Two fetal spleen lines are grown in “stromal medium,” which is described in example 2.

[0109] Non-adherent fetal stem cells attach to the stromal cells and form colonies (colony forming unit-CFU). Stromal cells and CFU are isolated by means of sterile glass cylinders and expanded in culture. A clone, called Fsp 62891, contains the flk-2 ligand. Fsp 62891 was deposited in the American Type Culture Collection, Rockville, Md., U.S.A on Nov. 21, 1991, accession number CRL 10935.

[0110] Fetal liver and fetal thymus cells are prepared in a similar way. Both of these cell types produce ligands of flk-1 and, in the case of liver, some flk-2. One such fetal thymus cell line, called F.thy 62891, and one such fetal liver cell line, called FL 62891, were deposited in the American Type Culture Collection, Rockville, Md., U.S.A on Nov. 21, 1991 and Apr. 2, 1992, respectively, accession numbers CRL 10936 and CRL 11005, respectively.

[0111] Stable human cell lines are prepared from fetal cells with the same temperature sensitive immortalizing virus used to prepare the murine cell line described in example 1.

Example 4 Isolation of Human Stromal Cell Clone

[0112] Highly retractile cells overgrow patches of stromal cells, presumably because the stromal cells produce factors that allow the formation of the CFU. To isolate stromal cell clones, sterile glass cylinders coated with vacuum grease are positioned over the CFU. A trypsin-EDTA solution (100 ml) is added in order to detach the cells. The cells are added to 5 ml of stromal medium and each (clone) plated in a single well of 6-well plate.

Example 5 Plasmid (AP-tag) for Expressing Secretable Alkaline Phosphatase (SEAP)

[0113] Plasmids that express secretable alkaline phosphatase are described by Flanagan and Leder in Cell 63, 185-194 (1990). The plasmids contain a promoter, such as the LTR promoter; a polylinker, including HindIII and BgIII; DNA encoding SEAP; a poly-A signal; and ampicillin resistance gene; and replication site.

Example 6 Plasmid for Expressing APtag-flk-2 and APtag-flk-1 Fusion Proteins

[0114] Plasmids that express fusion proteins of SEAP and the extracellular portion of either flk-1 or flk-2 are prepared in accordance with the protocols of Flanagan and Leder in Cell 63, 185-194 (1990) and Berger et al., Gene 66, 1-10 (1988). Briefly, a HindIII-Bam HI fragment containing the extracellular portion of flk-1 or flk-2 is prepared and inserted into the HindIII-BgIII site of the plasmid described in example 5.

Example 7 Production Of APtaq-1 Or -flk-2 Fusion Protein

[0115] The plasmids from Example 6 are transfected into Cos-7 cells by DEAE-dextran (as described in Current Protocols in Molecular Biology, Unit 16.13, “Transient Expression of Proteins Using Cos Cells,” 1991); and cotransfected with a selectable marker, such as pSV7neo, into NIH/3T3 cells by calcium precipitation. The NIH/3T3 cells are selected with 600 μg/ml G418 in 100 mm plates. Over 300 clones are screened for secretion of placental alkaline phosphatase activity. The assay is performed by heating a portion of the supernatant at 65° C. for 10 minutes to inactivate background phosphatase activity, and measuring the OD₄₀₅ after incubating with 1M diethanolamine (pH 9.8), 0.5 mM MgCl₂, 10 mM L-homoarginine (a phosphatase inhibitor), 0.5 mg/ml BSA, and 12 mM p-nitrophenyl phosphate. Human placental alkaline phosphatase is used to perform a standard curve. The APtaq-flk-1 clones (F-1AP21-4) produce up to 10 μg alkaline phosphatase activity/ml and the APtaq-flk-2 clones (F-2AP26-0) produce up to 0.5 μg alkaline phosphatase activity/ml.

Example 8 Assay For APtaq-flk-1 Or APtag-flk-2 Binding To Cells

[0116] The binding of APtaq-flk-1 or APtag-flk-2 to cells containing the appropriate ligand is assayed by standard methods. See, for example, Flanagan and Leder, Cell 63:185-194, 1990). Cells (i.e., mouse stromal cells, human fetal liver, spleen or thymus, or various control cells) are grown to confluency in six-well plates and washed with HBHA (Hank's balanced salt solution with 0.5 mg/ml BSA, 0.02% NaN₃, 20 mM HEPES, pH 7.0). Supernatants from transfected COS or NIH/3T3 cells containing either APtaq-flk-1 fusion protein, APtag-flk-2 fusion protein, or APtag without a receptor (as a control) are added to the cell monolayers and incubated for two hours at room temperature on a rotating platform. The concentration of the APtaq-flk-1 fusion protein, APtag-flk-2 fusion protein, or APtag without a receptor is 60 ng/ml of alkaline phosphatase as determined by the standard alkaline phosphatase curve (see above). The cells are then rinsed seven times with HBHA and lysed in 350 μl of 1% Triton X-100, 10 mM Tris-HCl (pH 8.0). The lysates are transferred to a microfuge tube, along with a further 150 μl rinse with the same solution. After vortexing vigorously, the samples are centrifuged for five minutes in a microfuge, heated at 65° C. for 12 minutes to inactivate cellular phosphatases, and assayed for phosphatase activity as described previously. Results of experiments designed to show the time and dose responses of binding between stromal cells containing the ligands to flk-2 and flk-1 (2018) and APtag-flk-2, APtag-flk-1 and APtag without receptor (as a control) are shown in FIGS. 3 and 4, respectively.

Example 8A Plasmids for Expressing flk1/fms and flk2/fms Fusion Proteins

[0117] Plasmids that express fusion proteins of the extracellular portion of either flk-1 or flk-2 and the intracellular portion of c-fms (also known as colony-stimulating factor-1 receptor) are prepared in a manner similar to that described under Example 6 (Plasmid for expressing APtag-flk-2 and APtag-flk-1 fusion proteins). Briefly, a Hind III-Bam HI fragment containing the extracellular portion of flk1 or flk2 is prepared and inserted into the Hind III-Bgl II site of a pLH expression vector containing the intracellular portion of c-fms.

8B Expression of flk1/fms or flk2/fms in 3T3 Cells

[0118] The plasmids from Example 11 are transfected into NIH/3T3 cells by calcium. The intracellular portion of c-fms is detected by Western blotting.

Example 9 Cloning and Expression of cDNA Coding For Mouse Ligand To flk-1 and flk-2 Receptors

[0119] cDNA expressing mouse ligand for flk-1 and flk-2 is prepared by known methods. See, for example, Seed, B., and Aruffo, A. PNAS 84:3365-3369, 1987; Simmons, D. and Seed, B. J. Immunol. 141:2797-2800; and D'Andrea, A. D., Lodish, H. F. and Wong, G. G. Cell 57:277-285, 1989).

[0120] The protocols are listed below in sequence: (a) RNA isolation; (b) poly A RNA preparation; (c) cDNA synthesis; (d) cDNA size fractionation; (e) propagation of plasmids (vector); (f) isolation of plasmid DNA; (g) preparation of vector pSV Sport (BRL Gibco) for cloning; (h) compilation of buffers for the above steps; (i) Transfection of cDNA encoding Ligands in Cos 7 Cells; (j) panning procedure; (k) Expression cloning of flk-1 or flk-2 ligand by establishment of an autocrine loop.

9a Guanidinium thiocyanate/LiCl Protocol for RNA Isolation

[0121] For each ml of mix desired, 0.5 g guanidine thiocyanate (GuSCN) is dissolved in 0.55 ml of 25% LiCl (stock filtered through 0.45 micron filter). 20 μl of mercaptoethanol is added. (The resulting solution is not good for more than about a week at room temperature.)

[0122] The 2018 stromal cells are centrifuged, and 1 ml of the solution described above is added to up to 5×10⁷ cells. The cells are sheared by means of a polytron until the mixture is non-viscous. For small scale preparations (<10⁸ cells), the sheared mixture is layered on 1.5 ml of 5.7M CsCl (RNase free; 1.26 g CsCl added to every ml 10 mM EDTA pH8), and overlaid with RNase-free water if needed. The mixture is spun in an SW55 rotor at 50 krpm for 2 hours. For large scale preparations, 25 ml of the mixture is layered on 12 ml CsCl in an SW28 tube, overlaid as above, and spun at 24 krpm for 8 hours. The contents of the tube are aspirated carefully with a sterile pasteur pipet connected to a vacuum flask. Once past the CsCl interface, a band around the tube is scratched with the pipet tip to prevent creeping of the layer on the wall down the tube. The remaining CsCl solution is aspirated. The resulting pellet is taken up in water, but not redissolved. 1/10 volume of sodium acetate and three volumes of ethanol are added to the mixture, and spun. The pellet is resuspended in water at 70° C., if necessary. The concentration of the RNA is adjusted to 1 mg/ml and frozen.

[0123] It should be noted that small RNA molecules (e.g., 5S) do not come down. For small amounts of cells, the volumes are scaled down, and the mixture is overlaid with GuSCN in RNase-free water on a gradient (precipitation is inefficient when RNA is dilute).

9b Poly A⁻ RNA Preparation

[0124] (All buffers mentioned are compiled separately below)

[0125] A disposable polypropylene column is prepared by washing with 5M NaOH and then rinsing with RNase-free water. For each milligram of total RNA, approximately 0.3 ml (final packed bed) of oligo dT cellulose is added. The oligo dT cellulose is prepared by resuspending approximately 0.5 ml of dry powder in 1 ml of 0.1M NaOH and transferring it into the column, or by percolating 0.1M NaOH through a previously used column. The column is washed with several column volumes of RNase-free water until the pH is neutral, and rinsed with 2-3 ml of loading buffer. The column bed is transferred to a sterile 15 ml tube using 4-6 ml of loading buffer.

[0126] Total RNA from the 2018 cell line is heated to 70° C. for 2-3 minutes. LiCl from RNase-free stock is added to the mixture to a final concentration of 0.5M. The mixture is combined with oligo dT cellulose in the 15 ml tube, which is vortexed or agitated for 10 minutes. The mixture is poured into the column, and washed with 3 ml loading buffer, and then with 3 ml of middle wash buffer. The mRNA is eluted directly into an SW55 tube with 1.5 ml of 2 mM EDTA and 0.1% SDS, discarding the first two or three drops.

[0127] The eluted mRNA is precipitated by adding {fraction (1/10)} volume of 3M sodium acetate and filling the tube with ethanol. The contents of the tube are mixed, chilled for 30 minutes at −20° C., and spun at 50 krpm at 5° C. for 30 minutes. After the ethanol is decanted, and the tube air dried, the mRNA pellet is resuspended in 50-100 μl of RNase-free water. 5 μl of the resuspended mRNA is heated to 70° C. in MOPS/EDTA/formaldehyde, and examined on an RNase-free 1% agarose gel.

9c cDNA Synthesis

[0128] The protocol used is a variation of the method described by Gubler and Hoffman in Gene 25, 263-270 (1983).

[0129] 1. First Strand. 4 μg of mRNA is added to a microfuge tube, heated to approximately 100° C. for 30 seconds, quenched on ice. The volume is adjusted to 70μl with RNAse-free water. 20 l of RT1 buffer, 2 μl of RNAse inhibitor (Boehringer 36 u/μl), 1 μl of 5 μg/μl of oligo dT (Collaborative Research), 2.5 μl of 20 mM dXTP's (ultrapure—US Biochemicals), 1 μl of 1M DTT and 4 μl of RT-XL (Life Sciences, 24 u/μl) are added. The mixture is incubated at 42° C. for 40 minutes, and inactivated by heating at 70° C. for 10 minutes.

[0130] 2. Second Strand. 320 μl of RNAse-free water, 80 μl of RT2 buffer, 5 μl of DNA Polymerase I (Boehringer, 5 U/μl), 2 μl RNAse H (BRL 2 u/μl) are added to the solution containing the first strand. The solution is incubated at 15° C. for one hour and at 22° C. for an additional hour. After adding 20 μl of 0.5M EDTA, pH 8.0, the solution is extracted with phenol and precipitated by adding NaCl to 0.5M linear polyacrylamide (carrier) to 20 μg/ml, and filling the tube with EtOH. The tube is spun for 2-3 minutes in a microfuge, vortexed to dislodge precipitated material from the wall of the tube, and respun for one minute.

[0131] 3. Adaptors. Adaptors provide specific restriction sites to facilitate cloning, and are available from BRL Gibco, New England Biolabs, etc. Crude adaptors are resuspended at a concentration of 1 μg/μl. MgSO₄ is added to a final concentration of 10 mM, followed by five volumes of EtCH. The resulting precipitate is rinsed with 70% EtOH and resuspended in TE at a concentration of 1 μg/μl. To kinase, 25 μl of resuspended adaptors is added to 3 μl of 10×kinasing buffer and 20 units of kinase. The mixture is incubated at 37° C. overnight. The precipitated cDNA is resuspended in 240 μl of TE (10/1). After adding 30 μl of 10×low salt buffer, 30 μl of 10×ligation buffer with 0.1 mM ATP, 3 μl (2.4 μg) of kinased 12-mer adaptor sequence, 2 μl (1.6 μg) of kinased 8-mer adaptor sequence, and 1 μl of T4 DNA ligase (BioLabs, 400 u/μl, or Boehringer, 1 Weiss unit ml), the mixture is incubated at 15° C. overnight. The cDNA is extracted with phenol and precipitated as above, except that the extra carrier is omitted, and resuspended in 100 μl of TE.

9d cDNA Size Fractionation

[0132] A 20% KOAc, 2 mM EDTA, 1 μg/ml ethidium bromide solution and a 5% KOAc, 2 mM EDTA, 1 μg/ml ethidium bromide solution are prepared. 2.6 ml of the 20% KOAc solution is added to the back chamber of a small gradient maker. Air bubbles are removed from the tube connecting the two chambers by allowing the 20% solution to flow into the front chamber and forcing the solution to return to the back chamber by tilting the gradient maker. The passage between the chambers is closed, and 2.5 ml of 5% solution is added to the front chamber. Any liquid in the tubing from a previous run is removed by allowing the 5% solution to flow to the end of the tubing, and then to return to its chamber. The apparatus is placed on a stirplate, and, with rapid stirring, the topcock connecting the two chambers and the front stopcock are opened. A polyallomer 5W55 tube is filled from the bottom with the KOAC solution. The gradient is overlaid with 100 μl of cDNA solution, and spun for three hours at 50 k rpm at 22° C. To collect fractions from the gradient, the SW55 tube is pierced close to the bottom of the tube with a butterfly infusion set (with the luer hub clipped off). Three 0.5 ml fractions and then six 0.25 ml fractions are collected in microfuge tubes (approximately 22 and 11 drops, respectively). The fractions are precipitated by adding linear polyacrylamide to 20 μg/ml and filling the tube to the top with ethanol. The tubes are cooled, spun in a microfuge tube for three minutes, vortexed, and respun for one minute. The resulting pellets are rinsed with 70% ethanol and respun, taking care not to permit the pellets to dry to completion. Each 0.25 ml fraction is resuspended in 10 μl of TE, and 1 μl is run on a 1% agarose minigel. The first three fractions, and the last six which contain no material smaller than 1 kb are pooled.

9e Propagation of Plasmids

[0133] SupF plasmids are selected in nonsuppressing bacterial hosts containing a second plasmid, p3, which contains amber mutated ampicillin and tetracycline drug resistance elements. See Seed, Nucleic Acids Res., 11, 2427-2445 (1983). The p3 plasmid is derived from RP1, is 57 kb in length, and is a stably maintained, single copy episome. The ampicillin resistance of this plasmid reverts at a high rate so that amp plasmids usually cannot be used in p3-containing strains. Selection for tetracycline resistance alone is almost as good as selection for ampicillin-tetracycline resistance. However, spontaneous appearance of chromosomal suppressor tRNA mutations presents an unavoidable background (frequency about 10⁻⁹) in this system. Colonies arising from spontaneous suppressor mutations are usually larger than colonies arising from plasmid transformation. Suppressor plasmids are selected in Luria broth (LB) medium containing ampicillin at 12.5 μg/ml and tetracycline at 7.5 μg/ml. For scaled-up plasmid preparations, M9 Casamino acids medium containing glycerol (0.8%) is employed as a carbon source. The bacteria are grown to saturation.

[0134] Alternatively, pSV Sport (BRL, Gaithersberg, Md.) may be employed to provide SV40 derived sequences for replication, transcription initiation and termination in COS 7 cells, as well as those sequences necessary for replication and ampicillin resistance in E. coli.

9f Isolation of Vector DNA/Plasmid

[0135] One liter of saturated bacterial cells are spun down in J6 bottles at 4.2 k rpm for 25 minutes. The cells are resuspended in 40 ml 10 mM EDTA, pH 8. 80 ml 0.2M NaOH and 1% SDS are added, and the mixture is swirled until it is clear and viscous. 40 ml 5M KOAc, pH 4.7 (2.5M KOAc, 2.5M HOAc) is added, and the mixture is shaken semi-vigorously until the lumps are approximately 2-3 mm in size. The bottle is spun at 4.2 k rpm for 5 minutes. The supernatant is poured through cheesecloth into a 250 ml bottle, which is then filled with isopropyl alcohol and centrifuged at 4.2 k rpm for 5 minutes. The bottle is gently drained and rinsed with 70% ethanol, taking care not to fragment the pellet. After inverting the bottle and removing traces of ethanol, the mixture is resuspended in 3.5 ml Tris base/EDTA (20 mM/10 mM). 3.75 ml of resuspended pellet and 0.75 ml 10 mg/ml ethidium bromide are added to 4.5 g CsCl. VTi80 tubes are filled with solution, and centrifuged for at least 2.5 hours at 80 k rpm. Bands are extracted by visible light with 1 ml syringe and 20 gauge or lower needle. The top of the tube is cut off with scissors, and the needle is inserted upwards into the tube at an angle of about 30 degrees with respect to the tube at a position about 3 mm beneath the band, with the bevel of the needle up. After the band is removed, the contents of the tube are poured into bleach. The extracted band is deposited in a 13 ml Sarstedt tube, which is then filled to the top with n-butanol saturated with 1M NaCl extract. If the amount of DNA is large, the extraction procedure may be repeated. After aspirating the butanol into a trap containing 5M NaOH to destroy ethidium, an approximately equal volume of 1M ammonium acetate and approximately two volumes of 95% ethanol are added to the DNA, which is then spun at 10 k rpm for 5 minutes. The pellet is rinsed carefully with 70% ethanol, and dried with a swab or lyophilizer.

9a Preparation of Vector for Cloning

[0136] 20 μg of vector is cut in a 200 μl reaction with 100 units of BstXI (New York Biolabs) at 50° C. overnight in a well thermostated, circulating water bath. Potassium acetate solutions (5 and 20%) are prepared in 5W55 tubes as described above. 100 μl of the digested vector is added to each tube and spun for three hours, 50 k rpm at 22° C. Under 300 m UV light, the desired band is observed to migrate ⅔ of the length of the tube. Forward trailing of the band indicates that the gradient is overloaded. The band is removed with a 1 ml syringe fitted with a 20 gauge needle. After adding linear polyacrylamide and precipitating the plasmid by adding three volumes of ethanol, the plasmid is resuspended in 50 μl of TE. Trial ligations are carried out with a constant amount of vector and increasing amounts of cDNA. Large scale ligation are carried out on the basis of these trial ligations. Usually the entire cDNA prep requires 1-2 μg of cut vector.

9h Buffers

[0137] Loading Buffer:0.5M LiCl, 10 mM Tris pH 7.5, 1 mM EDTA .1% SDS.

[0138] Middle Wash Buffer:0.15M LiCl, 10 mM Tris pH 7.5, 1 mM EDTA 0.1% SDS.

[0139] RT1 Buffer:0.25M Tris pH 8.8 (8.2 at 42⁻), 0.25M KCl, 30 mM MgCl₂.

[0140] RT2 Buffer:0.1M Tris pH 7.5, 25 mM MgCl2, 0.5M KCl, 0.25 mg/ml BSA, 50 mM dithiothreitol (DTT).

[0141] 10×Low Salt:60 mM Tris pH 7.5, 60 mM MgCl₂, 50 mM NaCl, 2.5 mg/ml BSA 70 mM DME

[0142] 10×Ligation Additions:1 mM ATP, 20 mM DTT, 1 mg/ml BSA 10 mM spermidine.

[0143] 10×Kinasing Buffer:0.5M Tris pH 7.5, 10 mM ATP, 20 mM DTT, 10 mM spermidine, 1 mg/ml BSA 100 mM MgCl2

9i Transfection of cDNA Encoding Ligands in Cos 7 Cells

[0144] Cos 7 cells are split 1:5 into 100 mm plates in Dulbecco's modified Eagles medium (DME)/10% fetal calf serum (FCS), and allowed to grow overnight. 3 ml Tris/DME (0.039M Tris, pH 7.4 in DME) containing 400 μg/ml DEAE-dextran (Sigma, D-9885) is prepared for each 100 mm plate of Cos 7 cells to be transfected. 10 μg of plasmid DNA preparation per plate is added. The medium is removed from the Cos-7 cells and the DNA/DEAE-dextran mixture is added. The cells are incubated for 4.5 hours. The medium is removed from the cells, and replaced with 3 ml of DME containing 2% fetal calf serum (FCS) and 0.1 mM chloroquine. The cells are incubated for one hour. After removing the chloroquine and replacing with 1.5 ml 20% glycerol in PBS, the cells are allowed to stand at room temperature for one minute. 3 ml Tris/DME is added, and the mixture is aspirated and washed two times with Tris/DME. 10 ml DME/10% FCS is added and the mixture is incubated overnight. The transfected Cos 7 cells are split 1:2 into fresh 100 mm plates with (DME)/10% FCS and allowed to grow.

9i Panning Procedure for Cos 7 Cells Expressing Ligand

[0145] 1) Antibody-coated plates

[0146] Bacteriological 100 mm plates are coated for 1.5 hours with rabbit anti-human placental alkaline phosphatase (Dako, Calif.) diluted 1:500 in 10 ml of 50 mM Tris.HCl, pH 9.5. The plates are washed three times with 0.15M NaCl, and incubated with 3 mg BSA/ml PBS overnight. The blocking solution is aspirated, and the plates are utilized immediately or frozen for later use.

[0147] 2) Panning cells

[0148] The medium from transfected Cos 7 cells is aspirated, and 3 ml PBS/0.5 mM EDTA/0.02% sodium azide is added. The plates are incubated at 37° C. for thirty minutes in order to detach the cells. The cells are triturated vigorously with a pasteur pipet and collected in a 15 ml centrifuge tube. The plate is washed with a further 2 ml PBS/EDTA/azide solution, which is then added to the centrifuge tube. After centrifuging at 200×g for five minutes, the cells are resuspended in 3 ml of APtaq-flk-1 (F-1AP21-4) or flk-2 (F-2AP26-0) supernatant from transfected NIH/3T3 cells (see Example 7.), and incubated for 1.5 hours on ice. The cells are centrifuged again at 200×g for five minutes. The supernatant is aspirated, and the cells are resuspended in 3 ml PBS/EDTA/azide solution. The cell suspension is layered carefully on 3 ml PBS/EDTA/azide/2% Ficoll, and centrifuged at 200×g for four minutes. The supernatant is aspirated, and the cells are resuspended in 0.5 ml PBS/EDTA/azide solution. The cells are added to the antibody-coated plates containing 4 ml PBS/EDTA/azide/5% FBS, and allowed to stand at room temperature one to three hours. Non-adhering cells are removed by washing gently two or three times with 3 ml PBS/5% FBS.

[0149] 3) Hirt Supernatant

[0150] 0.4 ml 0.6% SDS and 10 mM EDTA are added to the panned plates, which are allowed to stand 20 minutes. The viscuous mixture is added by means of a pipet into a microfuge tube. 0.1 ml 5M NaCl is added to the tube, mixed, and chilled on ice for at least five hours. The tube is spun for four minutes, and the supernatant is removed carefully. The contents of the tube are extracted with phenol once, or, if the first interface is not clean, twice. Ten micrograms of linear polyacrylamide (or other carrier) is added, and the tube is filled to the top with ethanol. The resulting precipitate is resuspended in 0.1 ml water or TE. After adding 3 volumes of EtOH/NaOAc, the cells are reprecipitated and resuspended in 0.1 ml water or TE. The cDNA obtained is transfected into any suitable E. coli host by electroporation. Suitable hosts are described in various catalogs, and include MC1061/p3 or Electromax DH10B Cells of BRL Gibco. The cDNA is extracted by conventional methods.

[0151] The above panning procedure is repeated until a pure E. coli clone bearing the cDNA as a unique plasmid recombinant capable of transfecting mammalian cells and yielding a positive panning assay is isolated. Normally, three repetitions are sufficient.

9k Expression Cloning of flk1 or flk2 Ligand by Establishment of an Autocrine Loop

[0152] Cells expressing flk1/fms or flk2/fms (Example 10) are transfected with 20-30 μg of a cDNA library from either flk1 ligand or flk2 ligand expressing stromal cells, respectively. The cDNA library is prepared as described above (a-h). The cells are co-transfected with 1 μg pLTR neo cDNA. Following transfection the cells are passaged 1:2 and cultured in 800 μg/ml of G418 in Dulbecco's medium (DME) supplemented with 10% CS. Approximately 12 days later the colonies of cells are passaged and plated onto dishes coated with poly -D- lysine (1 mg/ml) and human fibronectin (15 μg/ml). The culture medium is defined serum-free medium which is a mixture (3:1) of DME and Ham's F12 medium. The medium supplements are 8 mM NaHCO₃, 15 mM HEPES pH 7.4, 3 mM histidine, 4 μM MnCl₂, 10 μM ethanolamine, 0.1 μM selenous acid, 2 μM hydrocortisone, 5 μg/ml transferrin, 500 μg/ml bovine serum albumin/linoleic acid complex, and 20 μg/ml insulin (Ref. Zhan, X, et al. Oncogene 1: 369-376,1987). The cultures are refed the next day and every 3 days until the only cells capable of growing under the defined medium condition remain. The remaining colonies of cells are expanded and tested for the presence of the ligand by assaying for binding of APtag-flk1 or APtag-flk2 to the cells (as described in Example 8). The DNA would be rescued from cells demonstrating the presence of the flk1 or flk2 ligand and the sequence.

Example 10 Expression of Ligand cDNA

[0153] The cDNA is sequenced, and expressed in a suitable host cell, such as a mammalian cell, preferably COS, CHO or NIH/3T3 cells. The presence of the ligand is confirmed by demonstrating binding of the ligand to APtag-flk2 fusion protein (see above).

Example 11 Chemical Cross Linking of Receptor and Ligand

[0154] Cross linking experiments are performed on intact cells using a modification of the procedure described by Blume-Jensen et al et al., EMBO J., 10, 4121-4128 (1991). Cells are cultured in 100 mm tissue culture plates to subconfluence and washed once with PBS-0.1% BSA.

[0155] To examine chemical cross linking of soluble receptor to membrane-bound ligand, stromal cells from the 2018 stromal cell line are incubated with conditioned media (CM) from transfected 3T3 cells expressing the soluble receptor Flk2-APtag. Cross linking studies of soluble ligand to membrane bound receptor are performed by incubating conditioned media from 2018 cells with transfected 3T3 cells expressing a Flk2-fms fusion construct.

[0156] Binding is carried out for 2 hours either at room temperature with CM containing 0.02% sodium azide to prevent receptor internalization or at 4° C. with CM (and buffers) supplemented with sodium vanadate to prevent receptor dephosphorylation. Cells are washed twice with PBS-0.1% BSA and four times with PBS.

[0157] Cross linking is performed in PBS containing 250 mM disuccinimidyl suberate (DSS; Pierce) for 30 minutes at room temperature. The reaction is quenched with Tris-HCL pH7.4 to a final concentration of 50 mM.

[0158] Cells are solubilized in solubilization buffer: 0.5% Triton-X100, 0.5% deoxycholic acid, 20 mM Tris pH 7.4, 150 mM NaCl, 10 mM EDTA, 1 mM PMFS, 50 mg/ml aprotinin, 2 mg/ml bestatin, 2 mg/ml pepstatin and 10mg/ml leupeptin. Lysed cells are immediately transferred to 1.5 ml Nalgene tubes and solubilized by rolling end to end for 45 minutes at 4° C. Lysates are then centrifuged in a microfuge at 14,000 g for 10 minutes. Solubilized cross linked receptor complexes are then retrieved from lysates by incubating supernatants with 10% (v/v) wheat germ lectin-Sepharose 6MB beads (Pharmacia) at 4° C. for 2 hours or overnight.

[0159] Beads are washed once with Tris-buffered saline (TBS) and resuspended in 2×SDS-polyacrylamide nonreducing sample buffer. Bound complexes are eluted from the beads by heating at 95° C. for 5 minutes. Samples are analyzed on 4-12% gradient gels (NOVEX) under nonreducing and reducing conditions (0.35M 2-mercaptoethanol) and then transferred to PVDF membranes for 2 hours using a Novex blotting apparatus. Blots are blocked in TBS-3% BSA for 1 hour at room temperature followed by incubation with appropriate antibody.

[0160] Cross linked Flk2-APtag and Flk2-fms receptors are detected using rabbit polyclonal antibodies raised against human alkaline phosphatase and fms protein, respectively. The remainder of the procedure is carried out according to the instructions provided in the ABC Kit (Pierce). The kit is based on the use of a biotinylated secondary antibody and avidin-biotinylated horseradish peroxidase complex for detection.

Example 12 Expression and Purification of Flag-Flk-2

[0161] 1. Design of the Flag-Flk2 expression plasmids

[0162] A synthetic DNA fragment (Fragment 1) is synthesized using complementary oligonucleotides BP1 and BP2 (see below and SEQ. ID. NOS. 7 and 8). The fragment encoded the following features in the 5′ to 3′ order: Sal I restriction site, 22 base pair (bp) 5′ untranslated region containing an eukaryotic ribosome binding site, an ATG initiation codon, preprotrypsinogen signal sequence, coding region for the FLAG peptide (DYKDDDDKI) and Bgl II restriction site.

[0163] A cDNA fragment (Fragment 2) encoding Asn 27 to Ser 544 of murine Flk2 is obtained by polymerase chain reaction (PCR) using primers designed to introduce an in frame Bgl II site at the 5′ end (oligonucleotide BP5, see below and SEQ. ID. NO. 9) and a termination codon followed by a Not I site at the 3′ end (oligonucleotide BP10, see below and SEQ. ID. NO. 10). The template for the PCR reaction is full length Flk2 cDNA (Matthews et al., Cell 65:1143 (1991)). Fragment 2 is extensively digested with Bgl II and Not I restriction enzymes prior to ligation.

[0164] To assemble the complete Flag-Flk2 gene, Fragments 1 and 2 are ligated in a tripartate ligation into Sal I and Not I digested plasmid pSPORT (Gibco/BRL, Grand Island, N.Y.) to give the plasmid pFlag-Flk2.

[0165] Preferably, the Flag-Flk2 protein is attached at either end to the Fc portion of an immunoglobulin (Ig). The Ig is preferably attached to the Flk2 portion of the Flag-Flk2 protein. To assemble the construct pFlag-FLK2-Ig, the sequences coding for the CH¹ domain of human immunoglobulin G (IgG¹) are placed downstream of the Flk2 coding region in the plasmid pFlag-Flk2 as per the method described by Zettlemeissl et al., DNA and Cell Biology 9: 347-352 (1990).

[0166] The sequences of oligonucleotides used to construct the Flag-Flk2 gene are given below:

[0167] Oligonucleotide BP1:

[0168] 5′-AATTCGTCGACTTTCTGTCACCATGAGTGCACTTCTGATCCTAGCCCTTGTG GGAGCTGCTGTTGCTGACTACAAAGATGATGATGACAAGATCTA-3′

[0169] Oligonucleotide BP2:

[0170] 5′-AGCTTAGATCTTGTCATCATCATCTTTGTAGTCAGCAACAGCAGCTCCCACA AGGGCTAGGATCAGAAGTGCACTCATGGTGACAGAAAGTCGACG-3′

[0171] Oligonucleotide BP5:

[0172] 5′-TGAGAAGATCTCAAACCAAGACCTGCCTGT-3′

[0173] Oligonucleotide BP10:

[0174] 5′-CCAATGGCGGCCGCTCAGGAGATGTTGTCTTGGA-3′

[0175] 2. Expression of the Flag-Flk2 construct

[0176] For transient expression of the Flag-Flk2 construct, the Sal1 to Not I fragment from pFlag-Flk2 is subcloned into the plasmid pSVSPORT (Gibco/BRL) to give the plasmid pSVFlag-Flk2. For expression of the Flag-Flk2 protein pSVFlag-Flk2 is transfected into COS monkey cells using the DEAE-dextran method.

[0177] For stable expression in eukaryotic cells, the Sal I-Not I fragment of pFlag-Flk2 is cloned into the EcoRV and Not I sites of the plasmid pcDNA I/Neo (Invitrogen Co., San Diego, Calif.). The Sal I 3′ recessed terminus of pFlag-Flk2 is filled with the Klenow fragment of DNA polymerase I and a mixture of deoxyribonucleotides to make the site compatible with the EcoRV site of the vector. The resulting construct is introduced into cultured mamalian cells using either the Lipofectin (Gibco/BRL) or the calcium phosphate methods.

[0178] For expression in insect cells, the Sal I to Hind III (from pSPORT polylinker) fragment of pFlag-Flk2 is subcloned into the BamH1-Hind III sites of the baculovirus transfer vector pBlueBac III (Invitrogen). The vector Bam HI site and the insert Sal I site are blunted with Klenow (see above). Production of the recombinant virus and infection of the Sf9 insect cells is performed as per manufacturers directions (Invitrogen).

[0179] Expression of the Flag-Flk2 protein is detected by Western blotting of SDS-PAGE separated conditioned media (mamalian cells) or cell lysates (insect cells) with the anti-Flag monoclonal antibody (mAb) M1 (International Biotechnology, Inc. [IBI], New Haven, Conn.).

[0180] 3. Affinity purification of the Flag-Flk2 protein from conditioned media or insect cell lysates is performed using immobilized mAb M1 (IBI) as per manufacturers specifications.

[0181] 3.1 Affinity purification of the Flag-Flk2-Ig¹ protein from conditioned media is performed using immobilized Protein A (Pharmacia LKB, Piscataway, N.J.) as per the manufacturers instructions.

[0182] II. Use of the Flag-Flk2 protein to search for the Flk2 ligand

[0183] 1. Binding and cross-linking studies to detect membrane-bound ligand

[0184] A. Binding studies

[0185] Murine stromal lines (eg. 2018 cells ATCC CRL 10907 (see below), see example 1, supra) considered to be candidates for expression of the Flk2 ligand were deposited at the American Type Culture Collection, ATCC CRL 10907 (see below) and cultured in Dulbecco's modified Eagles medium (DMEM; Gibco/BRL) supplemented with 10% fetal calf serum. The cells are grown to confluency in 10 cm plates and washed once with PBS. Conditioned media containing Flag-Flk2 is incubated with the cells at 4° C. for 2 hrs. The cell monolayers are rinsed extensively to remove the non-bound protein, solubilized and centrifuged to remove insoluble cellular material. Glycoproteins in the lysates are partially purified with wheat germ agglutinin-Sepharose (Pharmacia LKB, Piscataway, N.J.), boiled in an SDS sample buffer, separated on SDS-PAGE gels and transferred to nitrocellulose membranes. The membranes are probed with the M1 antibody to detect the presence of cell-associated Flag-Flk2 protein.

[0186] B. In a cross-linking study, the above protocol is followed except that prior to solubilization the monolayer are treated with the crosslinker disuccinimidyl suberate (DSS; Pierce, Rockford, Ill.). The presence of a putative ligand is detected by an upward shift in the apparent molecular weight of the Flag-Flk2 band on Western blots.

[0187] C. Purified Flag-Flk2 protein labelled with Na125I via the Chloramine T method is used to asses the ability of the soluble extracellular domain of the Flk2 receptor to bind transmembrane form of the Flk2 ligand in cultured stromal lines. The labelled protein is added to monolayers of stromal cells on ice for 2 hr in the presence or absence of excess unlabelled protein. Specific binding is calculated by subtracting counts bound in the presence of excess unlabelled protein from the total counts bound.

[0188] 2. Use of the Flag-Flk2 protein to search for secreted form of the ligand

[0189] A. The Flag-Flk2 protein is used in attempts to identify the Flk2 ligand in conditioned media from stromal cell cultures via modification of the direct N-terminal sequencing method of Pan et al., Bioch. Biophys. Res. Comm. 166:201 (1990). Briefly, the Flag-Flk2 protein N-terminally sequenced by automatic Edman degradation chemistry an an ABI 477A sequncer with on line PTH amino acid analysis. Approximatelly 15 amino acids are determined. The protein is then immobilized on Nugel PAF silica beads via free NH4+ groups. The immobilized Flag-Flk2 is incubated with conditioned media from putative ligand-producing cells for 30 min at 4° C. and washed free off non-bound proteins with phosphate buffered saline adjusted to 2M NaCl. The resulting protein complex is resequenced. For each sequencing cycle, any amino acid not expected at this position in the FLAG-Flk2 protein is considered as possibly originating from a protein complexed to the Flk2 receptor.

[0190] B. For conventional affinity chromatography, the Flag-Flk2 protein is immobilized on a stable support such as Sepharose. 35S-methionine labelled-conditioned media from stromal cell lines are passed over the affinity matrix and bound material is analyzed by SDS-PAGE gel electrophoresis and autoradiography.

[0191] 3. Use of the Flag-Flk2 protein in expression cloning experiments

[0192] A method of expression cloning of integral membrane proteins in COS cells has been described (Aruffo and Seed, Proc. Natl. Acad. Sci. 84:8573 (1987)). A cDNA library is prepared from an appropriate stromal cell line such as 2018 and is transfected into COS cells. Cells transiently expressing the Flk2 ligand are affinity adsorbed onto plastic plates coated with the Flag-Flk2 protein. The cells are lysed, the plasmid DNA is recovered and amplified in a bacterial host. The cycle of transfection into Cos cells is repeated until a single cDNA clone encoding the ligand molecule is isolated.

[0193] In a modification of the above technique, pools of transfected COS cells are screened for binding of 125I-Flag-Flk2. Positive cells pools are selected and plasmid DNA is recovered and amplified in E. coli. The resulting DNA preparation is used in subsequent rounds of transfection and transient expression until all cells are positive for binding of 125I-Flag-Flk2. The cDNA in the final plasmid preparation is then sequenced to determine the sequnce of the putative Flk-2 ligand.

Supplemental Enablement

[0194] The invention as claimed is enabled in accordance with the above specification and readily available references and starting materials. Nevertheless, Applicants have deposited with the American Type Culture Collection, Rockville, Md., USA (ATCC) the cell lines listed below:

[0195] 2018, ATCC accession no. CRL 10907, deposited Oct. 30, 1991.

[0196] Fsp 62891, ATCC accession no. CRL 10935, deposited Nov. 21, 1991.

[0197] F.thy 62891, ATCC accession no. CRL 10936, deposited Nov. 21, 1991.

[0198] FL 62891, ATCC accession no. CRL 11005, deposited Apr. 2, 1992.

[0199] These deposits were made under the provisions of the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purposes of Patent Procedure and the regulations thereunder (Budapest Treaty). This assures maintenance of a viable culture for 30 years from date of deposit. The organisms will be made available by ATCC under the terms of the Budapest Treaty, and subject to an agreement between Applicants and ATCC which assures unrestricted availability upon issuance of the pertinent U.S. patent. Availability of the deposited strains is not to be construed as a license to practice the invention in contravention of the rights granted under the authority of any government in accordance with its patent laws.

1 10 3453 base pairs nucleic acid double linear cDNA NO NO N-terminal mat_peptide 112..3006 sig_peptide 31..111 CDS 31..3009 1 GCGGCCTGGC TACCGCGCGC TCCGGAGGCC ATG CGG GCG TTG GCG CAG CGC AGC 54 Met Arg Ala Leu Ala Gln Arg Ser -27 -25 -20 GAC CGG CGG CTG CTG CTG CTT GTT GTT TTG TCA GTA ATG ATT CTT GAG 102 Asp Arg Arg Leu Leu Leu Leu Val Val Leu Ser Val Met Ile Leu Glu -15 -10 -5 ACC GTT ACA AAC CAA GAC CTG CCT GTG ATC AAG TGT GTT TTA ATC AGT 150 Thr Val Thr Asn Gln Asp Leu Pro Val Ile Lys Cys Val Leu Ile Ser 1 5 10 CAT GAG AAC AAT GGC TCA TCA GCG GGA AAG CCA TCA TCG TAC CGA ATG 198 His Glu Asn Asn Gly Ser Ser Ala Gly Lys Pro Ser Ser Tyr Arg Met 15 20 25 GTG CGA GGA TCC CCA GAA GAC CTC CAG TGT ACC CCG AGG CGC CAG AGT 246 Val Arg Gly Ser Pro Glu Asp Leu Gln Cys Thr Pro Arg Arg Gln Ser 30 35 40 45 GAA GGG ACG GTA TAT GAA GCG GCC ACC GTG GAG GTG GCC GAG TCT GGG 294 Glu Gly Thr Val Tyr Glu Ala Ala Thr Val Glu Val Ala Glu Ser Gly 50 55 60 TCC ATC ACC CTG CAA GTG CAG CTC GCC ACC CCA GGG GAC CTT TCC TGC 342 Ser Ile Thr Leu Gln Val Gln Leu Ala Thr Pro Gly Asp Leu Ser Cys 65 70 75 CTC TGG GTC TTT AAG CAC AGC TCC CTG GGC TGC CAG CCG CAC TTT GAT 390 Leu Trp Val Phe Lys His Ser Ser Leu Gly Cys Gln Pro His Phe Asp 80 85 90 TTA CAA AAC AGA GGA ATC GTT TCC ATG GCC ATC TTG AAC GTG ACA GAG 438 Leu Gln Asn Arg Gly Ile Val Ser Met Ala Ile Leu Asn Val Thr Glu 95 100 105 ACC CAG GCA GGA GAA TAC CTA CTC CAT ATT CAG AGC GAA CGC GCC AAC 486 Thr Gln Ala Gly Glu Tyr Leu Leu His Ile Gln Ser Glu Arg Ala Asn 110 115 120 125 TAC ACA GTA CTG TTC ACA GTG AAT GTA AGA GAT ACA CAG CTG TAT GTG 534 Tyr Thr Val Leu Phe Thr Val Asn Val Arg Asp Thr Gln Leu Tyr Val 130 135 140 CTA AGG AGA CCT TAC TTT AGG AAG ATG GAA AAC CAG GAT GCA CTG CTC 582 Leu Arg Arg Pro Tyr Phe Arg Lys Met Glu Asn Gln Asp Ala Leu Leu 145 150 155 TGC ATC TCC GAG GGT GTT CCG GAG CCC ACT GTG GAG TGG GTG CTC TGC 630 Cys Ile Ser Glu Gly Val Pro Glu Pro Thr Val Glu Trp Val Leu Cys 160 165 170 AGC TCC CAC AGG GAA AGC TGT AAA GAA GAA GGC CCT GCT GTT GTC AGA 678 Ser Ser His Arg Glu Ser Cys Lys Glu Glu Gly Pro Ala Val Val Arg 175 180 185 AAG GAG GAA AAG GTA CTT CAT GAG TTG TTC GGA ACA GAC ATC AGA TGC 726 Lys Glu Glu Lys Val Leu His Glu Leu Phe Gly Thr Asp Ile Arg Cys 190 195 200 205 TGT GCT AGA AAT GCA CTG GGC CGC GAA TGC ACC AAG CTG TTC ACC ATA 774 Cys Ala Arg Asn Ala Leu Gly Arg Glu Cys Thr Lys Leu Phe Thr Ile 210 215 220 GAT CTA AAC CAG GCT CCT CAG AGC ACA CTG CCC CAG TTA TTC CTG AAA 822 Asp Leu Asn Gln Ala Pro Gln Ser Thr Leu Pro Gln Leu Phe Leu Lys 225 230 235 GTG GGG GAA CCC TTG TGG ATC AGG TGT AAG GCC ATC CAT GTG AAC CAT 870 Val Gly Glu Pro Leu Trp Ile Arg Cys Lys Ala Ile His Val Asn His 240 245 250 GGA TTC GGG CTC ACC TGG GAG CTG GAA GAC AAA GCC CTG GAG GAG GGC 918 Gly Phe Gly Leu Thr Trp Glu Leu Glu Asp Lys Ala Leu Glu Glu Gly 255 260 265 AGC TAC TTT GAG ATG AGT ACC TAC TCC ACA AAC AGG ACC ATG ATT CGG 966 Ser Tyr Phe Glu Met Ser Thr Tyr Ser Thr Asn Arg Thr Met Ile Arg 270 275 280 285 ATT CTC TTG GCC TTT GTG TCT TCC GTG GGA AGG AAC GAC ACC GGA TAT 1014 Ile Leu Leu Ala Phe Val Ser Ser Val Gly Arg Asn Asp Thr Gly Tyr 290 295 300 TAC ACC TGC TCT TCC TCA AAG CAC CCC AGC CAG TCA GCG TTG GTG ACC 1062 Tyr Thr Cys Ser Ser Ser Lys His Pro Ser Gln Ser Ala Leu Val Thr 305 310 315 ATC CTA GAA AAA GGG TTT ATA AAC GCT ACC AGC TCG CAA GAA GAG TAT 1110 Ile Leu Glu Lys Gly Phe Ile Asn Ala Thr Ser Ser Gln Glu Glu Tyr 320 325 330 GAA ATT GAC CCG TAC GAA AAG TTC TGC TTC TCA GTC AGG TTT AAA GCG 1158 Glu Ile Asp Pro Tyr Glu Lys Phe Cys Phe Ser Val Arg Phe Lys Ala 335 340 345 TAC CCA CGA ATC CGA TGC ACG TGG ATC TTC TCT CAA GCC TCA TTT CCT 1206 Tyr Pro Arg Ile Arg Cys Thr Trp Ile Phe Ser Gln Ala Ser Phe Pro 350 355 360 365 TGT GAA CAG AGA GGC CTG GAG GAT GGG TAC AGC ATA TCT AAA TTT TGC 1254 Cys Glu Gln Arg Gly Leu Glu Asp Gly Tyr Ser Ile Ser Lys Phe Cys 370 375 380 GAT CAT AAG AAC AAG CCA GGA GAG TAC ATA TTC TAT GCA GAA AAT GAT 1302 Asp His Lys Asn Lys Pro Gly Glu Tyr Ile Phe Tyr Ala Glu Asn Asp 385 390 395 GAC GCC CAG TTC ACC AAA ATG TTC ACG CTG AAT ATA AGA AAG AAA CCT 1350 Asp Ala Gln Phe Thr Lys Met Phe Thr Leu Asn Ile Arg Lys Lys Pro 400 405 410 CAA GTG CTA GCA AAT GCC TCA GCC AGC CAG GCG TCC TGT TCC TCT GAT 1398 Gln Val Leu Ala Asn Ala Ser Ala Ser Gln Ala Ser Cys Ser Ser Asp 415 420 425 GGC TAC CCG CTA CCC TCT TGG ACC TGG AAG AAG TGT TCG GAC AAA TCT 1446 Gly Tyr Pro Leu Pro Ser Trp Thr Trp Lys Lys Cys Ser Asp Lys Ser 430 435 440 445 CCC AAT TGC ACG GAG GAA ATC CCA GAA GGA GTT TGG AAT AAA AAG GCT 1494 Pro Asn Cys Thr Glu Glu Ile Pro Glu Gly Val Trp Asn Lys Lys Ala 450 455 460 AAC AGA AAA GTG TTT GGC CAG TGG GTG TCG AGC AGT ACT CTA AAT ATG 1542 Asn Arg Lys Val Phe Gly Gln Trp Val Ser Ser Ser Thr Leu Asn Met 465 470 475 AGT GAG GCC GGG AAA GGG CTT CTG GTC AAA TGC TGT GCG TAC AAT TCT 1590 Ser Glu Ala Gly Lys Gly Leu Leu Val Lys Cys Cys Ala Tyr Asn Ser 480 485 490 ATG GGC ACG TCT TGC GAA ACC ATC TTT TTA AAC TCA CCA GGC CCC TTC 1638 Met Gly Thr Ser Cys Glu Thr Ile Phe Leu Asn Ser Pro Gly Pro Phe 495 500 505 CCT TTC ATC CAA GAC AAC ATC TCC TTC TAT GCG ACC ATT GGG CTC TGT 1686 Pro Phe Ile Gln Asp Asn Ile Ser Phe Tyr Ala Thr Ile Gly Leu Cys 510 515 520 525 CTC CCC TTC ATT GTT GTT CTC ATT GTG TTG ATC TGC CAC AAA TAC AAA 1734 Leu Pro Phe Ile Val Val Leu Ile Val Leu Ile Cys His Lys Tyr Lys 530 535 540 AAG CAA TTT AGG TAC GAG AGT CAG CTG CAG ATG ATC CAG GTG ACT GGC 1782 Lys Gln Phe Arg Tyr Glu Ser Gln Leu Gln Met Ile Gln Val Thr Gly 545 550 555 CCC CTG GAT AAC GAG TAC TTC TAC GTT GAC TTC AGG GAC TAT GAA TAT 1830 Pro Leu Asp Asn Glu Tyr Phe Tyr Val Asp Phe Arg Asp Tyr Glu Tyr 560 565 570 GAC CTT AAG TGG GAG TTC CCG AGA GAG AAC TTA GAG TTT GGG AAG GTC 1878 Asp Leu Lys Trp Glu Phe Pro Arg Glu Asn Leu Glu Phe Gly Lys Val 575 580 585 CTG GGG TCT GGC GCT TTC GGG AGG GTG ATG AAC GCC ACG GCC TAT GGC 1926 Leu Gly Ser Gly Ala Phe Gly Arg Val Met Asn Ala Thr Ala Tyr Gly 590 595 600 605 ATT AGT AAA ACG GGA GTC TCA ATT CAG GTG GCG GTG AAG ATG CTA AAA 1974 Ile Ser Lys Thr Gly Val Ser Ile Gln Val Ala Val Lys Met Leu Lys 610 615 620 GAG AAA GCT GAC AGC TGT GAA AAA GAA GCT CTC ATG TCG GAG CTC AAA 2022 Glu Lys Ala Asp Ser Cys Glu Lys Glu Ala Leu Met Ser Glu Leu Lys 625 630 635 ATG ATG ACC CAC CTG GGA CAC CAT GAC AAC ATC GTG AAT CTG CTG GGG 2070 Met Met Thr His Leu Gly His His Asp Asn Ile Val Asn Leu Leu Gly 640 645 650 GCA TGC ACA CTG TCA GGG CCA GTG TAC TTG ATT TTT GAA TAT TGT TGC 2118 Ala Cys Thr Leu Ser Gly Pro Val Tyr Leu Ile Phe Glu Tyr Cys Cys 655 660 665 TAT GGT GAC CTC CTC AAC TAC CTA AGA AGT AAA AGA GAG AAG TTT CAC 2166 Tyr Gly Asp Leu Leu Asn Tyr Leu Arg Ser Lys Arg Glu Lys Phe His 670 675 680 685 AGG ACA TGG ACA GAG ATT TTT AAG GAA CAT AAT TTC AGT TCT TAC CCT 2214 Arg Thr Trp Thr Glu Ile Phe Lys Glu His Asn Phe Ser Ser Tyr Pro 690 695 700 ACT TTC CAG GCA CAT TCA AAT TCC AGC ATG CCT GGT TCA CGA GAA GTT 2262 Thr Phe Gln Ala His Ser Asn Ser Ser Met Pro Gly Ser Arg Glu Val 705 710 715 CAG TTA CAC CCG CCC TTG GAT CAG CTC TCA GGG TTC AAT GGG AAT TCA 2310 Gln Leu His Pro Pro Leu Asp Gln Leu Ser Gly Phe Asn Gly Asn Ser 720 725 730 ATT CAT TCT GAA GAT GAG ATT GAA TAT GAA AAC CAG AAG AGG CTG GCA 2358 Ile His Ser Glu Asp Glu Ile Glu Tyr Glu Asn Gln Lys Arg Leu Ala 735 740 745 GAA GAA GAG GAG GAA GAT TTG AAC GTG CTG ACG TTT GAA GAC CTC CTT 2406 Glu Glu Glu Glu Glu Asp Leu Asn Val Leu Thr Phe Glu Asp Leu Leu 750 755 760 765 TGC TTT GCG TAC CAA GTG GCC AAA GGC ATG GAA TTC CTG GAG TTC AAG 2454 Cys Phe Ala Tyr Gln Val Ala Lys Gly Met Glu Phe Leu Glu Phe Lys 770 775 780 TCG TGT GTC CAC AGA GAC CTG GCA GCC AGG AAT GTG TTG GTC ACC CAC 2502 Ser Cys Val His Arg Asp Leu Ala Ala Arg Asn Val Leu Val Thr His 785 790 795 GGG AAG GTG GTG AAG ATC TGT GAC TTT GGA CTG GCC CGA GAC ATC CTG 2550 Gly Lys Val Val Lys Ile Cys Asp Phe Gly Leu Ala Arg Asp Ile Leu 800 805 810 AGC GAC TCC AGC TAC GTC GTC AGG GGC AAC GCA CGG CTG CCG GTG AAG 2598 Ser Asp Ser Ser Tyr Val Val Arg Gly Asn Ala Arg Leu Pro Val Lys 815 820 825 TGG ATG GCA CCC GAG AGC TTA TTT GAA GGG ATC TAC ACA ATC AAG AGT 2646 Trp Met Ala Pro Glu Ser Leu Phe Glu Gly Ile Tyr Thr Ile Lys Ser 830 835 840 845 GAC GTC TGG TCC TAC GGC ATC CTT CTC TGG GAG ATA TTT TCA CTG GGT 2694 Asp Val Trp Ser Tyr Gly Ile Leu Leu Trp Glu Ile Phe Ser Leu Gly 850 855 860 GTG AAC CCT TAC CCT GGC ATT CCT GTC GAC GCT AAC TTC TAT AAA CTG 2742 Val Asn Pro Tyr Pro Gly Ile Pro Val Asp Ala Asn Phe Tyr Lys Leu 865 870 875 ATT CAG AGT GGA TTT AAA ATG GAG CAG CCA TTC TAT GCC ACA GAA GGG 2790 Ile Gln Ser Gly Phe Lys Met Glu Gln Pro Phe Tyr Ala Thr Glu Gly 880 885 890 ATA TAC TTT GTA ATG CAA TCC TGC TGG GCT TTT GAC TCA AGG AAG CGG 2838 Ile Tyr Phe Val Met Gln Ser Cys Trp Ala Phe Asp Ser Arg Lys Arg 895 900 905 CCA TCC TTC CCC AAC CTG ACT TCA TTT TTA GGA TGT CAG CTG GCA GAG 2886 Pro Ser Phe Pro Asn Leu Thr Ser Phe Leu Gly Cys Gln Leu Ala Glu 910 915 920 925 GCA GAA GAA GCA TGT ATC AGA ACA TCC ATC CAT CTA CCA AAA CAG GCG 2934 Ala Glu Glu Ala Cys Ile Arg Thr Ser Ile His Leu Pro Lys Gln Ala 930 935 940 GCC CCT CAG CAG AGA GGC GGG CTC AGA GCC CAG TCG CCA CAG CGC CAG 2982 Ala Pro Gln Gln Arg Gly Gly Leu Arg Ala Gln Ser Pro Gln Arg Gln 945 950 955 GTG AAG ATT CAC AGA GAA AGA AGT TAGCGAGGAG GCCTTGGACC CCGCCACCC 3036 Val Lys Ile His Arg Glu Arg Ser 960 965 AGCAGGCTGT AGACCGCAGA GCCAAGATTA GCCTCGCCTC TGAGGAAGCG CCCTACAG 3096 CGTTGCTTCG CTGGACTTTT CTCTAGATGC TGTCTGCCAT TACTCCAAAG TGACTTCT 3156 AAAATCAAAC CTCTCCTCGC ACAGGCGGGA GAGCCAATAA TGAGACTTGT TGGTGAGC 3216 GCCTACCCTG GGGGCCTTTC CACGAGCTTG AGGGGAAAGC CATGTATCTG AAATATAG 3276 TATTCTTGTA AATACGTGAA ACAAACCAAA CCCGTTTTTT GCTAAGGGAA AGCTAAAT 3336 GATTTTTAAA AATCTATGTT TTAAAATACT ATGTAACTTT TTCATCTATT TAGTGATA 3396 TTTTATGGAT GGAAATAAAC TTTCTACTGT AAAAAAAAAA AAAAAAAAAA AAAAAAA 3453 992 amino acids amino acid linear protein 2 Met Arg Ala Leu Ala Gln Arg Ser Asp Arg Arg Leu Leu Leu Leu Val -27 -25 -20 -15 Val Leu Ser Val Met Ile Leu Glu Thr Val Thr Asn Gln Asp Leu Pro -10 -5 1 5 Val Ile Lys Cys Val Leu Ile Ser His Glu Asn Asn Gly Ser Ser Ala 10 15 20 Gly Lys Pro Ser Ser Tyr Arg Met Val Arg Gly Ser Pro Glu Asp Leu 25 30 35 Gln Cys Thr Pro Arg Arg Gln Ser Glu Gly Thr Val Tyr Glu Ala Ala 40 45 50 Thr Val Glu Val Ala Glu Ser Gly Ser Ile Thr Leu Gln Val Gln Leu 55 60 65 Ala Thr Pro Gly Asp Leu Ser Cys Leu Trp Val Phe Lys His Ser Ser 70 75 80 85 Leu Gly Cys Gln Pro His Phe Asp Leu Gln Asn Arg Gly Ile Val Ser 90 95 100 Met Ala Ile Leu Asn Val Thr Glu Thr Gln Ala Gly Glu Tyr Leu Leu 105 110 115 His Ile Gln Ser Glu Arg Ala Asn Tyr Thr Val Leu Phe Thr Val Asn 120 125 130 Val Arg Asp Thr Gln Leu Tyr Val Leu Arg Arg Pro Tyr Phe Arg Lys 135 140 145 Met Glu Asn Gln Asp Ala Leu Leu Cys Ile Ser Glu Gly Val Pro Glu 150 155 160 165 Pro Thr Val Glu Trp Val Leu Cys Ser Ser His Arg Glu Ser Cys Lys 170 175 180 Glu Glu Gly Pro Ala Val Val Arg Lys Glu Glu Lys Val Leu His Glu 185 190 195 Leu Phe Gly Thr Asp Ile Arg Cys Cys Ala Arg Asn Ala Leu Gly Arg 200 205 210 Glu Cys Thr Lys Leu Phe Thr Ile Asp Leu Asn Gln Ala Pro Gln Ser 215 220 225 Thr Leu Pro Gln Leu Phe Leu Lys Val Gly Glu Pro Leu Trp Ile Arg 230 235 240 245 Cys Lys Ala Ile His Val Asn His Gly Phe Gly Leu Thr Trp Glu Leu 250 255 260 Glu Asp Lys Ala Leu Glu Glu Gly Ser Tyr Phe Glu Met Ser Thr Tyr 265 270 275 Ser Thr Asn Arg Thr Met Ile Arg Ile Leu Leu Ala Phe Val Ser Ser 280 285 290 Val Gly Arg Asn Asp Thr Gly Tyr Tyr Thr Cys Ser Ser Ser Lys His 295 300 305 Pro Ser Gln Ser Ala Leu Val Thr Ile Leu Glu Lys Gly Phe Ile Asn 310 315 320 325 Ala Thr Ser Ser Gln Glu Glu Tyr Glu Ile Asp Pro Tyr Glu Lys Phe 330 335 340 Cys Phe Ser Val Arg Phe Lys Ala Tyr Pro Arg Ile Arg Cys Thr Trp 345 350 355 Ile Phe Ser Gln Ala Ser Phe Pro Cys Glu Gln Arg Gly Leu Glu Asp 360 365 370 Gly Tyr Ser Ile Ser Lys Phe Cys Asp His Lys Asn Lys Pro Gly Glu 375 380 385 Tyr Ile Phe Tyr Ala Glu Asn Asp Asp Ala Gln Phe Thr Lys Met Phe 390 395 400 405 Thr Leu Asn Ile Arg Lys Lys Pro Gln Val Leu Ala Asn Ala Ser Ala 410 415 420 Ser Gln Ala Ser Cys Ser Ser Asp Gly Tyr Pro Leu Pro Ser Trp Thr 425 430 435 Trp Lys Lys Cys Ser Asp Lys Ser Pro Asn Cys Thr Glu Glu Ile Pro 440 445 450 Glu Gly Val Trp Asn Lys Lys Ala Asn Arg Lys Val Phe Gly Gln Trp 455 460 465 Val Ser Ser Ser Thr Leu Asn Met Ser Glu Ala Gly Lys Gly Leu Leu 470 475 480 485 Val Lys Cys Cys Ala Tyr Asn Ser Met Gly Thr Ser Cys Glu Thr Ile 490 495 500 Phe Leu Asn Ser Pro Gly Pro Phe Pro Phe Ile Gln Asp Asn Ile Ser 505 510 515 Phe Tyr Ala Thr Ile Gly Leu Cys Leu Pro Phe Ile Val Val Leu Ile 520 525 530 Val Leu Ile Cys His Lys Tyr Lys Lys Gln Phe Arg Tyr Glu Ser Gln 535 540 545 Leu Gln Met Ile Gln Val Thr Gly Pro Leu Asp Asn Glu Tyr Phe Tyr 550 555 560 565 Val Asp Phe Arg Asp Tyr Glu Tyr Asp Leu Lys Trp Glu Phe Pro Arg 570 575 580 Glu Asn Leu Glu Phe Gly Lys Val Leu Gly Ser Gly Ala Phe Gly Arg 585 590 595 Val Met Asn Ala Thr Ala Tyr Gly Ile Ser Lys Thr Gly Val Ser Ile 600 605 610 Gln Val Ala Val Lys Met Leu Lys Glu Lys Ala Asp Ser Cys Glu Lys 615 620 625 Glu Ala Leu Met Ser Glu Leu Lys Met Met Thr His Leu Gly His His 630 635 640 645 Asp Asn Ile Val Asn Leu Leu Gly Ala Cys Thr Leu Ser Gly Pro Val 650 655 660 Tyr Leu Ile Phe Glu Tyr Cys Cys Tyr Gly Asp Leu Leu Asn Tyr Leu 665 670 675 Arg Ser Lys Arg Glu Lys Phe His Arg Thr Trp Thr Glu Ile Phe Lys 680 685 690 Glu His Asn Phe Ser Ser Tyr Pro Thr Phe Gln Ala His Ser Asn Ser 695 700 705 Ser Met Pro Gly Ser Arg Glu Val Gln Leu His Pro Pro Leu Asp Gln 710 715 720 725 Leu Ser Gly Phe Asn Gly Asn Ser Ile His Ser Glu Asp Glu Ile Glu 730 735 740 Tyr Glu Asn Gln Lys Arg Leu Ala Glu Glu Glu Glu Glu Asp Leu Asn 745 750 755 Val Leu Thr Phe Glu Asp Leu Leu Cys Phe Ala Tyr Gln Val Ala Lys 760 765 770 Gly Met Glu Phe Leu Glu Phe Lys Ser Cys Val His Arg Asp Leu Ala 775 780 785 Ala Arg Asn Val Leu Val Thr His Gly Lys Val Val Lys Ile Cys Asp 790 795 800 805 Phe Gly Leu Ala Arg Asp Ile Leu Ser Asp Ser Ser Tyr Val Val Arg 810 815 820 Gly Asn Ala Arg Leu Pro Val Lys Trp Met Ala Pro Glu Ser Leu Phe 825 830 835 Glu Gly Ile Tyr Thr Ile Lys Ser Asp Val Trp Ser Tyr Gly Ile Leu 840 845 850 Leu Trp Glu Ile Phe Ser Leu Gly Val Asn Pro Tyr Pro Gly Ile Pro 855 860 865 Val Asp Ala Asn Phe Tyr Lys Leu Ile Gln Ser Gly Phe Lys Met Glu 870 875 880 885 Gln Pro Phe Tyr Ala Thr Glu Gly Ile Tyr Phe Val Met Gln Ser Cys 890 895 900 Trp Ala Phe Asp Ser Arg Lys Arg Pro Ser Phe Pro Asn Leu Thr Ser 905 910 915 Phe Leu Gly Cys Gln Leu Ala Glu Ala Glu Glu Ala Cys Ile Arg Thr 920 925 930 Ser Ile His Leu Pro Lys Gln Ala Ala Pro Gln Gln Arg Gly Gly Leu 935 940 945 Arg Ala Gln Ser Pro Gln Arg Gln Val Lys Ile His Arg Glu Arg Ser 950 955 960 965 3501 base pairs nucleic acid double linear cDNA NO NO N-terminal CDS 58..3039 mat_peptide 139..3036 sig_peptide 58..138 3 CGAGGCGGCA TCCGAGGGCT GGGCCGGCGC CCTGGGGGAC CCCGGGCTCC GGAGGCC 57 ATG CCG GCG TTG GCG CGC GAC GCG GGC ACC GTG CCG CTG CTC GTT GTT 105 Met Pro Ala Leu Ala Arg Asp Ala Gly Thr Val Pro Leu Leu Val Val -27 -25 -20 -15 TTT TCT GCA ATG ATA TTT GGG ACT ATT ACA AAT CAA GAT CTG CCT GTG 153 Phe Ser Ala Met Ile Phe Gly Thr Ile Thr Asn Gln Asp Leu Pro Val -10 -5 1 5 ATC AAG TGT GTT TTA ATC AAT CAT AAG AAC AAT GAT TCA TCA GTG GGG 201 Ile Lys Cys Val Leu Ile Asn His Lys Asn Asn Asp Ser Ser Val Gly 10 15 20 AAG TCA TCA TCA TAT CCC ATG GTA TCA GAA TCC CCG GAA GAC CTC GGG 249 Lys Ser Ser Ser Tyr Pro Met Val Ser Glu Ser Pro Glu Asp Leu Gly 25 30 35 TGT GCG TTG AGA CCC CAG AGC TCA GGG ACA GTG TAC GAA GCT GCC GCT 297 Cys Ala Leu Arg Pro Gln Ser Ser Gly Thr Val Tyr Glu Ala Ala Ala 40 45 50 GTG GAA GTG GAT GTA TCT GCT TCC ATC ACA CTG CAA GTG CTG GTC GAT 345 Val Glu Val Asp Val Ser Ala Ser Ile Thr Leu Gln Val Leu Val Asp 55 60 65 GCC CCA GGG AAC ATT TCC TGT CTC TGG GTC TTT AAG CAC AGC TCC CTG 393 Ala Pro Gly Asn Ile Ser Cys Leu Trp Val Phe Lys His Ser Ser Leu 70 75 80 85 AAT TGC CAG CCA CAT TTT GAT TTA CAA AAC AGA GGA GTT GTT TCC ATG 441 Asn Cys Gln Pro His Phe Asp Leu Gln Asn Arg Gly Val Val Ser Met 90 95 100 GTC ATT TTG AAA ATG ACA GAA ACC CAA GCT GGA GAA TAC CTA CTT TTT 489 Val Ile Leu Lys Met Thr Glu Thr Gln Ala Gly Glu Tyr Leu Leu Phe 105 110 115 ATT CAG AGT GAA GCT ACC AAT TAC ACA ATA TTG TTT ACA GTG AGT ATA 537 Ile Gln Ser Glu Ala Thr Asn Tyr Thr Ile Leu Phe Thr Val Ser Ile 120 125 130 AGA AAT ACC CTG CTT TAC ACA TTA AGA AGA CCT TAC TTT AGA AAA ATG 585 Arg Asn Thr Leu Leu Tyr Thr Leu Arg Arg Pro Tyr Phe Arg Lys Met 135 140 145 GAA AAC CAG GAC GCC CTG GTC TGC ATA TCT GAG AGC GTT CCA GAG CCG 633 Glu Asn Gln Asp Ala Leu Val Cys Ile Ser Glu Ser Val Pro Glu Pro 150 155 160 165 ATC GTG GAA TGG GTG CTT TGC GAT TCA CAG GGG GAA AGC TGT AAA GAA 681 Ile Val Glu Trp Val Leu Cys Asp Ser Gln Gly Glu Ser Cys Lys Glu 170 175 180 GAA AGT CCA GCT GTT GTT AAA AAG GAG GAA AAA GTG CTT CAT GAA TTA 729 Glu Ser Pro Ala Val Val Lys Lys Glu Glu Lys Val Leu His Glu Leu 185 190 195 TTT GGG ACG GAC ATA AGG TGC TGT GCC AGA AAT GAA CTG GGC AGG GAA 777 Phe Gly Thr Asp Ile Arg Cys Cys Ala Arg Asn Glu Leu Gly Arg Glu 200 205 210 TGC ACC AGG CTG TTC ACA ATA GAT CTA AAT CAA ACT CCT CAG ACC ACA 825 Cys Thr Arg Leu Phe Thr Ile Asp Leu Asn Gln Thr Pro Gln Thr Thr 215 220 225 TTG CCA CAA TTA TTT CTT AAA GTA GGG GAA CCC TTA TGG ATA AGG TGC 873 Leu Pro Gln Leu Phe Leu Lys Val Gly Glu Pro Leu Trp Ile Arg Cys 230 235 240 245 AAA GCT GTT CAT GTG AAC CAT GGA TTC GGG CTC ACC TGG GAA TTA GAA 921 Lys Ala Val His Val Asn His Gly Phe Gly Leu Thr Trp Glu Leu Glu 250 255 260 AAC AAA GCA CTC GAG GAG GGC AAC TAC TTT GAG ATG AGT ACC TAT TCA 969 Asn Lys Ala Leu Glu Glu Gly Asn Tyr Phe Glu Met Ser Thr Tyr Ser 265 270 275 ACA AAC AGA ACT ATG ATA CGG ATT CTG TTT GCT TTT GTA TCA TCA GTG 1017 Thr Asn Arg Thr Met Ile Arg Ile Leu Phe Ala Phe Val Ser Ser Val 280 285 290 GCA AGA AAC GAC ACC GGA TAC TAC ACT TGT TCC TCT TCA AAG CAT CCC 1065 Ala Arg Asn Asp Thr Gly Tyr Tyr Thr Cys Ser Ser Ser Lys His Pro 295 300 305 AGT CAA TCA GCT TTG GTT ACC ATC GTA GGA AAG GGA TTT ATA AAT GCT 1113 Ser Gln Ser Ala Leu Val Thr Ile Val Gly Lys Gly Phe Ile Asn Ala 310 315 320 325 ACC AAT TCA AGT GAA GAT TAT GAA ATT GAC CAA TAT GAA GAG TTT TGT 1161 Thr Asn Ser Ser Glu Asp Tyr Glu Ile Asp Gln Tyr Glu Glu Phe Cys 330 335 340 TTT TCT GTC AGG TTT AAA GCC TAC CCA CAA ATC AGA TGT ACG TGG ACC 1209 Phe Ser Val Arg Phe Lys Ala Tyr Pro Gln Ile Arg Cys Thr Trp Thr 345 350 355 TTC TCT CGA AAA TCA TTT CCT TGT GAG CAA AAG GGT CTT GAT AAC GGA 1257 Phe Ser Arg Lys Ser Phe Pro Cys Glu Gln Lys Gly Leu Asp Asn Gly 360 365 370 TAC AGC ATA TCC AAG TTT TGC AAT CAT AAG CAC CAG CCA GGA GAA TAT 1305 Tyr Ser Ile Ser Lys Phe Cys Asn His Lys His Gln Pro Gly Glu Tyr 375 380 385 ATA TTC CAT GCA GAA AAT GAT GAT GCC CAA TTT ACC AAA ATG TTC ACG 1353 Ile Phe His Ala Glu Asn Asp Asp Ala Gln Phe Thr Lys Met Phe Thr 390 395 400 405 CTG AAT ATA AGA AGG AAA CCT CAA GTG CTC GCA GAA GCA TCG GCA AGT 1401 Leu Asn Ile Arg Arg Lys Pro Gln Val Leu Ala Glu Ala Ser Ala Ser 410 415 420 CAG GCG TCC TGT TTC TCG GAT GGA TAC CCA TTA CCA TCT TGG ACC TGG 1449 Gln Ala Ser Cys Phe Ser Asp Gly Tyr Pro Leu Pro Ser Trp Thr Trp 425 430 435 AAG AAG TGT TCA GAC AAG TCT CCC AAC TGC ACA GAA GAG ATC ACA GAA 1497 Lys Lys Cys Ser Asp Lys Ser Pro Asn Cys Thr Glu Glu Ile Thr Glu 440 445 450 GGA GTC TGG AAT AGA AAG GCT AAC AGA AAA GTG TTT GGA CAG TGG GTG 1545 Gly Val Trp Asn Arg Lys Ala Asn Arg Lys Val Phe Gly Gln Trp Val 455 460 465 TCG AGC AGT ACT CTA AAC ATG AGT GAA GCC ATA AAA GGG TTC CTG GTC 1593 Ser Ser Ser Thr Leu Asn Met Ser Glu Ala Ile Lys Gly Phe Leu Val 470 475 480 485 AAG TGC TGT GCA TAC AAT TCC CTT GGC ACA TCT TGT GAG ACG ATC CTT 1641 Lys Cys Cys Ala Tyr Asn Ser Leu Gly Thr Ser Cys Glu Thr Ile Leu 490 495 500 TTA AAC TCT CCA GGC CCC TTC CCT TTC ATC CAA GAC AAC ATC TCA TTC 1689 Leu Asn Ser Pro Gly Pro Phe Pro Phe Ile Gln Asp Asn Ile Ser Phe 505 510 515 TAT GCA ACA ATT GGT GTT TGT CTC CTC TTC ATT GTC GTT TTA ACC CTG 1737 Tyr Ala Thr Ile Gly Val Cys Leu Leu Phe Ile Val Val Leu Thr Leu 520 525 530 CTA ATT TGT CAC AAG TAC AAA AAG CAA TTT AGG TAT GAA AGC CAG CTA 1785 Leu Ile Cys His Lys Tyr Lys Lys Gln Phe Arg Tyr Glu Ser Gln Leu 535 540 545 CAG ATG GTA CAG GTG ACC GGC TCC TCA GAT AAT GAG TAC TTC TAC GTT 1833 Gln Met Val Gln Val Thr Gly Ser Ser Asp Asn Glu Tyr Phe Tyr Val 550 555 560 565 GAT TTC AGA GAA TAT GAA TAT GAT CTC AAA TGG GAG TTT CCA AGA GAA 1881 Asp Phe Arg Glu Tyr Glu Tyr Asp Leu Lys Trp Glu Phe Pro Arg Glu 570 575 580 AAT TTA GAG TTT GGG AAG GTA CTA GGA TCA GGT GCT TTT GGA AAA GTG 1929 Asn Leu Glu Phe Gly Lys Val Leu Gly Ser Gly Ala Phe Gly Lys Val 585 590 595 ATG AAC GCA ACA GCT TAT GGA ATT AGC AAA ACA GGA GTC TCA ATC CAG 1977 Met Asn Ala Thr Ala Tyr Gly Ile Ser Lys Thr Gly Val Ser Ile Gln 600 605 610 GTT GCC GTC AAA ATG CTG AAA GAA AAA GCA GAC AGC TCT GAA AGA GAG 2025 Val Ala Val Lys Met Leu Lys Glu Lys Ala Asp Ser Ser Glu Arg Glu 615 620 625 GCA CTC ATG TCA GAA CTC AAG ATG ATG ACC CAG CTG GGA AGC CAC GAG 2073 Ala Leu Met Ser Glu Leu Lys Met Met Thr Gln Leu Gly Ser His Glu 630 635 640 645 AAT ATT GTG AAC CTG CTG GGG GCG TGC ACA CTG TCA GGA CCA ATT TAC 2121 Asn Ile Val Asn Leu Leu Gly Ala Cys Thr Leu Ser Gly Pro Ile Tyr 650 655 660 TTG ATT TTT GAA TAC TGT TGC TAT GGT GAT CTT CTC AAC TAT CTA AGA 2169 Leu Ile Phe Glu Tyr Cys Cys Tyr Gly Asp Leu Leu Asn Tyr Leu Arg 665 670 675 AGT AAA AGA GAA AAA TTT CAC AGG ACT TGG ACA GAG ATT TTC AAG GAA 2217 Ser Lys Arg Glu Lys Phe His Arg Thr Trp Thr Glu Ile Phe Lys Glu 680 685 690 CAC AAT TTC AGT TTT TAC CCC ACT TTC CAA TCA CAT CCA AAT TCC AGC 2265 His Asn Phe Ser Phe Tyr Pro Thr Phe Gln Ser His Pro Asn Ser Ser 695 700 705 ATG CCT GGT TCA AGA GAA GTT CAG ATA CAC CCG GAC TCG GAT CAA ATC 2313 Met Pro Gly Ser Arg Glu Val Gln Ile His Pro Asp Ser Asp Gln Ile 710 715 720 725 TCA GGG CTT CAT GGG AAT TCA TTT CAC TCT GAA GAT GAA ATT GAA TAT 2361 Ser Gly Leu His Gly Asn Ser Phe His Ser Glu Asp Glu Ile Glu Tyr 730 735 740 GAA AAC CAA AAA AGG CTG GAA GAA GAG GAG GAC TTG AAT GTG CTT ACA 2409 Glu Asn Gln Lys Arg Leu Glu Glu Glu Glu Asp Leu Asn Val Leu Thr 745 750 755 TTT GAA GAT CTT CTT TGC TTT GCA TAT CAA GTT GCC AAA GGA ATG GAA 2457 Phe Glu Asp Leu Leu Cys Phe Ala Tyr Gln Val Ala Lys Gly Met Glu 760 765 770 TTT CTG GAA TTT AAG TCG TGT GTT CAC AGA GAC CTG GCC GCC AGG AAC 2505 Phe Leu Glu Phe Lys Ser Cys Val His Arg Asp Leu Ala Ala Arg Asn 775 780 785 GTG CTT GTC ACC CAC GGG AAA GTG GTG AAG ATA TGT GAC TTT GGA TTG 2553 Val Leu Val Thr His Gly Lys Val Val Lys Ile Cys Asp Phe Gly Leu 790 795 800 805 GCT CGA GAT ATC ATG AGT GAT TCC AAC TAT GTT GTC AGG GGC AAT GCC 2601 Ala Arg Asp Ile Met Ser Asp Ser Asn Tyr Val Val Arg Gly Asn Ala 810 815 820 CGT CTG CCT GTA AAA TGG ATG GCC CCC GAA AGC CTG TTT GAA GGC ATC 2649 Arg Leu Pro Val Lys Trp Met Ala Pro Glu Ser Leu Phe Glu Gly Ile 825 830 835 TAC ACC ATT AAG AGT GAT GTC TGG TCA TAT GGA ATA TTA CTG TGG GAA 2697 Tyr Thr Ile Lys Ser Asp Val Trp Ser Tyr Gly Ile Leu Leu Trp Glu 840 845 850 ATC TTC TCA CTT GGT GTG AAT CCT TAC CCT GGC ATT CCG GTT GAT GCT 2745 Ile Phe Ser Leu Gly Val Asn Pro Tyr Pro Gly Ile Pro Val Asp Ala 855 860 865 AAC TTC TAC AAA CTG ATT CAA AAT GGA TTT AAA ATG GAT CAG CCA TTT 2793 Asn Phe Tyr Lys Leu Ile Gln Asn Gly Phe Lys Met Asp Gln Pro Phe 870 875 880 885 TAT GCT ACA GAA GAA ATA TAC ATT ATA ATG CAA TCC TGC TGG GCT TTT 2841 Tyr Ala Thr Glu Glu Ile Tyr Ile Ile Met Gln Ser Cys Trp Ala Phe 890 895 900 GAC TCA AGG AAA CGG CCA TCC TTC CCT AAT TTG ACT TCG TTT TTA GGA 2889 Asp Ser Arg Lys Arg Pro Ser Phe Pro Asn Leu Thr Ser Phe Leu Gly 905 910 915 TGT CAG CTG GCA GAT GCA GAA GAA GCG ATG TAT CAG AAT GTG GAT GGC 2937 Cys Gln Leu Ala Asp Ala Glu Glu Ala Met Tyr Gln Asn Val Asp Gly 920 925 930 CGT GTT TCG GAA TGT CCT CAC ACC TAC CAA AAC AGG CGA CCT TTC AGC 2985 Arg Val Ser Glu Cys Pro His Thr Tyr Gln Asn Arg Arg Pro Phe Ser 935 940 945 AGA GAG ATG GAT TTG GGG CTA CTC TCT CCG CAG GCT CAG GTC GAA GAT 3033 Arg Glu Met Asp Leu Gly Leu Leu Ser Pro Gln Ala Gln Val Glu Asp 950 955 960 965 TCG TAGAGGAACA ATTTAGTTTT AAGGACTTCA TCCCTCCACC TATCCCTAAC 3086 Ser AGGCTGTAGA TTACCAAAAC AAGATTAATT TCATCACTAA AAGAAAATCT ATTATCAA 3146 GCTGCTTCAC CAGACTTTTC TCTAGAAGCC GTCTGCGTTT ACTCTTGTTT TCAAAGGG 3206 TTTTGTAAAA TCAAATCATC CTGTCACAAG GCAGGAGGAG CTGATAATGA ACTTTATT 3266 AGCATTGATC TGCATCCAAG GCCTTCTCAG GCCGGCTTGA GTGAATTGTG TACCTGAA 3326 ACAGTATATT CTTGTAAATA CATAAAACAA AAGCATTTTG CTAAGGAGAA GCTAATAT 3386 TTTTTTAAGT CTATGTTTTA AAATAATATG TAAATTTTTC AGCTATTTAG TGATATAT 3446 TATGGGTGGG AATAAAATTT CTACTACAGA AAAAAAAAAA AAAAAAAAAA AAAAA 3501 993 amino acids amino acid linear protein 4 Met Pro Ala Leu Ala Arg Asp Ala Gly Thr Val Pro Leu Leu Val Val -27 -25 -20 -15 Phe Ser Ala Met Ile Phe Gly Thr Ile Thr Asn Gln Asp Leu Pro Val -10 -5 1 5 Ile Lys Cys Val Leu Ile Asn His Lys Asn Asn Asp Ser Ser Val Gly 10 15 20 Lys Ser Ser Ser Tyr Pro Met Val Ser Glu Ser Pro Glu Asp Leu Gly 25 30 35 Cys Ala Leu Arg Pro Gln Ser Ser Gly Thr Val Tyr Glu Ala Ala Ala 40 45 50 Val Glu Val Asp Val Ser Ala Ser Ile Thr Leu Gln Val Leu Val Asp 55 60 65 Ala Pro Gly Asn Ile Ser Cys Leu Trp Val Phe Lys His Ser Ser Leu 70 75 80 85 Asn Cys Gln Pro His Phe Asp Leu Gln Asn Arg Gly Val Val Ser Met 90 95 100 Val Ile Leu Lys Met Thr Glu Thr Gln Ala Gly Glu Tyr Leu Leu Phe 105 110 115 Ile Gln Ser Glu Ala Thr Asn Tyr Thr Ile Leu Phe Thr Val Ser Ile 120 125 130 Arg Asn Thr Leu Leu Tyr Thr Leu Arg Arg Pro Tyr Phe Arg Lys Met 135 140 145 Glu Asn Gln Asp Ala Leu Val Cys Ile Ser Glu Ser Val Pro Glu Pro 150 155 160 165 Ile Val Glu Trp Val Leu Cys Asp Ser Gln Gly Glu Ser Cys Lys Glu 170 175 180 Glu Ser Pro Ala Val Val Lys Lys Glu Glu Lys Val Leu His Glu Leu 185 190 195 Phe Gly Thr Asp Ile Arg Cys Cys Ala Arg Asn Glu Leu Gly Arg Glu 200 205 210 Cys Thr Arg Leu Phe Thr Ile Asp Leu Asn Gln Thr Pro Gln Thr Thr 215 220 225 Leu Pro Gln Leu Phe Leu Lys Val Gly Glu Pro Leu Trp Ile Arg Cys 230 235 240 245 Lys Ala Val His Val Asn His Gly Phe Gly Leu Thr Trp Glu Leu Glu 250 255 260 Asn Lys Ala Leu Glu Glu Gly Asn Tyr Phe Glu Met Ser Thr Tyr Ser 265 270 275 Thr Asn Arg Thr Met Ile Arg Ile Leu Phe Ala Phe Val Ser Ser Val 280 285 290 Ala Arg Asn Asp Thr Gly Tyr Tyr Thr Cys Ser Ser Ser Lys His Pro 295 300 305 Ser Gln Ser Ala Leu Val Thr Ile Val Gly Lys Gly Phe Ile Asn Ala 310 315 320 325 Thr Asn Ser Ser Glu Asp Tyr Glu Ile Asp Gln Tyr Glu Glu Phe Cys 330 335 340 Phe Ser Val Arg Phe Lys Ala Tyr Pro Gln Ile Arg Cys Thr Trp Thr 345 350 355 Phe Ser Arg Lys Ser Phe Pro Cys Glu Gln Lys Gly Leu Asp Asn Gly 360 365 370 Tyr Ser Ile Ser Lys Phe Cys Asn His Lys His Gln Pro Gly Glu Tyr 375 380 385 Ile Phe His Ala Glu Asn Asp Asp Ala Gln Phe Thr Lys Met Phe Thr 390 395 400 405 Leu Asn Ile Arg Arg Lys Pro Gln Val Leu Ala Glu Ala Ser Ala Ser 410 415 420 Gln Ala Ser Cys Phe Ser Asp Gly Tyr Pro Leu Pro Ser Trp Thr Trp 425 430 435 Lys Lys Cys Ser Asp Lys Ser Pro Asn Cys Thr Glu Glu Ile Thr Glu 440 445 450 Gly Val Trp Asn Arg Lys Ala Asn Arg Lys Val Phe Gly Gln Trp Val 455 460 465 Ser Ser Ser Thr Leu Asn Met Ser Glu Ala Ile Lys Gly Phe Leu Val 470 475 480 485 Lys Cys Cys Ala Tyr Asn Ser Leu Gly Thr Ser Cys Glu Thr Ile Leu 490 495 500 Leu Asn Ser Pro Gly Pro Phe Pro Phe Ile Gln Asp Asn Ile Ser Phe 505 510 515 Tyr Ala Thr Ile Gly Val Cys Leu Leu Phe Ile Val Val Leu Thr Leu 520 525 530 Leu Ile Cys His Lys Tyr Lys Lys Gln Phe Arg Tyr Glu Ser Gln Leu 535 540 545 Gln Met Val Gln Val Thr Gly Ser Ser Asp Asn Glu Tyr Phe Tyr Val 550 555 560 565 Asp Phe Arg Glu Tyr Glu Tyr Asp Leu Lys Trp Glu Phe Pro Arg Glu 570 575 580 Asn Leu Glu Phe Gly Lys Val Leu Gly Ser Gly Ala Phe Gly Lys Val 585 590 595 Met Asn Ala Thr Ala Tyr Gly Ile Ser Lys Thr Gly Val Ser Ile Gln 600 605 610 Val Ala Val Lys Met Leu Lys Glu Lys Ala Asp Ser Ser Glu Arg Glu 615 620 625 Ala Leu Met Ser Glu Leu Lys Met Met Thr Gln Leu Gly Ser His Glu 630 635 640 645 Asn Ile Val Asn Leu Leu Gly Ala Cys Thr Leu Ser Gly Pro Ile Tyr 650 655 660 Leu Ile Phe Glu Tyr Cys Cys Tyr Gly Asp Leu Leu Asn Tyr Leu Arg 665 670 675 Ser Lys Arg Glu Lys Phe His Arg Thr Trp Thr Glu Ile Phe Lys Glu 680 685 690 His Asn Phe Ser Phe Tyr Pro Thr Phe Gln Ser His Pro Asn Ser Ser 695 700 705 Met Pro Gly Ser Arg Glu Val Gln Ile His Pro Asp Ser Asp Gln Ile 710 715 720 725 Ser Gly Leu His Gly Asn Ser Phe His Ser Glu Asp Glu Ile Glu Tyr 730 735 740 Glu Asn Gln Lys Arg Leu Glu Glu Glu Glu Asp Leu Asn Val Leu Thr 745 750 755 Phe Glu Asp Leu Leu Cys Phe Ala Tyr Gln Val Ala Lys Gly Met Glu 760 765 770 Phe Leu Glu Phe Lys Ser Cys Val His Arg Asp Leu Ala Ala Arg Asn 775 780 785 Val Leu Val Thr His Gly Lys Val Val Lys Ile Cys Asp Phe Gly Leu 790 795 800 805 Ala Arg Asp Ile Met Ser Asp Ser Asn Tyr Val Val Arg Gly Asn Ala 810 815 820 Arg Leu Pro Val Lys Trp Met Ala Pro Glu Ser Leu Phe Glu Gly Ile 825 830 835 Tyr Thr Ile Lys Ser Asp Val Trp Ser Tyr Gly Ile Leu Leu Trp Glu 840 845 850 Ile Phe Ser Leu Gly Val Asn Pro Tyr Pro Gly Ile Pro Val Asp Ala 855 860 865 Asn Phe Tyr Lys Leu Ile Gln Asn Gly Phe Lys Met Asp Gln Pro Phe 870 875 880 885 Tyr Ala Thr Glu Glu Ile Tyr Ile Ile Met Gln Ser Cys Trp Ala Phe 890 895 900 Asp Ser Arg Lys Arg Pro Ser Phe Pro Asn Leu Thr Ser Phe Leu Gly 905 910 915 Cys Gln Leu Ala Asp Ala Glu Glu Ala Met Tyr Gln Asn Val Asp Gly 920 925 930 Arg Val Ser Glu Cys Pro His Thr Tyr Gln Asn Arg Arg Pro Phe Ser 935 940 945 Arg Glu Met Asp Leu Gly Leu Leu Ser Pro Gln Ala Gln Val Glu Asp 950 955 960 965 Ser 5406 base pairs nucleic acid double linear cDNA NO NO N-terminal CDS 208..4311 mat_peptide 265..4308 sig_peptide 208..264 5 CTGTGTCCCG CAGCCGGATA ACCTGGCTGA CCCGATTCCG CGGACACCCG TGCAGCCGCG 60 GCTGGAGCCA GGGCGCCGGT GCCCGCGCTC TCCCCGGTCT TGCGCTGCGG GGGCCGATA 120 CGCCTCTGTG ACTTCTTTGC GGGCCAGGGA CGGAGAAGGA GTCTGTGCCT GAGAAACTG 180 GCTCTGTGCC CAGGCGCGAG GTGCAGG ATG GAG AGC AAG GGC CTG CTA GCT 231 Met Glu Ser Lys Gly Leu Leu Ala -19 -15 GTC GCT CTG TGG TTC TGC GTG GAG ACC CGA GCC GCC TCT GTG GGT TTG 279 Val Ala Leu Trp Phe Cys Val Glu Thr Arg Ala Ala Ser Val Gly Leu -10 -5 1 5 CCT GGC GAT TTT CTC CAT CCC CCC AAG CTC AGC ACA CAG AAA GAC ATA 327 Pro Gly Asp Phe Leu His Pro Pro Lys Leu Ser Thr Gln Lys Asp Ile 10 15 20 CTG ACA ATT TTG GCA AAT ACA ACC CTT CAG ATT ACT TGC AGG GGA CAG 375 Leu Thr Ile Leu Ala Asn Thr Thr Leu Gln Ile Thr Cys Arg Gly Gln 25 30 35 CGG GAC CTG GAC TGG CTT TGG CCC AAT GCT CAG CGT GAT TCT GAG GAA 423 Arg Asp Leu Asp Trp Leu Trp Pro Asn Ala Gln Arg Asp Ser Glu Glu 40 45 50 AGG GTA TTG GTG ACT GAA TGC GGC GGT GGT GAC AGT ATC TTC TGC AAA 471 Arg Val Leu Val Thr Glu Cys Gly Gly Gly Asp Ser Ile Phe Cys Lys 55 60 65 ACA CTC ACC ATT CCC AGG GTG GTT GGA AAT GAT ACT GGA GCC TAC AAG 519 Thr Leu Thr Ile Pro Arg Val Val Gly Asn Asp Thr Gly Ala Tyr Lys 70 75 80 85 TGC TCG TAC CGG GAC GTC GAC ATA GCC TCC ACT GTT TAT GTC TAT GTT 567 Cys Ser Tyr Arg Asp Val Asp Ile Ala Ser Thr Val Tyr Val Tyr Val 90 95 100 CGA GAT TAC AGA TCA CCA TTC ATC GCC TCT GTC AGT GAC CAG CAT GGC 615 Arg Asp Tyr Arg Ser Pro Phe Ile Ala Ser Val Ser Asp Gln His Gly 105 110 115 ATC GTG TAC ATC ACC GAG AAC AAG AAC AAA ACT GTG GTG ATC CCC TGC 663 Ile Val Tyr Ile Thr Glu Asn Lys Asn Lys Thr Val Val Ile Pro Cys 120 125 130 CGA GGG TCG ATT TCA AAC CTC AAT GTG TCT CTT TGC GCT AGG TAT CCA 711 Arg Gly Ser Ile Ser Asn Leu Asn Val Ser Leu Cys Ala Arg Tyr Pro 135 140 145 GAA AAG AGA TTT GTT CCG GAT GGA AAC AGA ATT TCC TGG GAC AGC GAG 759 Glu Lys Arg Phe Val Pro Asp Gly Asn Arg Ile Ser Trp Asp Ser Glu 150 155 160 165 ATA GGC TTT ACT CTC CCC AGT TAC ATG ATC AGC TAT GCC GGC ATG GTC 807 Ile Gly Phe Thr Leu Pro Ser Tyr Met Ile Ser Tyr Ala Gly Met Val 170 175 180 TTC TGT GAG GCA AAG ATC AAT GAT GAA ACC TAT CAG TCT ATC ATG TAC 855 Phe Cys Glu Ala Lys Ile Asn Asp Glu Thr Tyr Gln Ser Ile Met Tyr 185 190 195 ATA GTT GTG GTT GTA GGA TAT AGG ATT TAT GAT GTG ATT CTG AGC CCC 903 Ile Val Val Val Val Gly Tyr Arg Ile Tyr Asp Val Ile Leu Ser Pro 200 205 210 CCG CAT GAA ATT GAG CTA TCT GCC GGA GAA AAA CTT GTC TTA AAT TGT 951 Pro His Glu Ile Glu Leu Ser Ala Gly Glu Lys Leu Val Leu Asn Cys 215 220 225 ACA GCG AGA ACA GAG CTC AAT GTG GGG CTT GAT TTC ACC TGG CAC TCT 999 Thr Ala Arg Thr Glu Leu Asn Val Gly Leu Asp Phe Thr Trp His Ser 230 235 240 245 CCA CCT TCA AAG TCT CAT CAT AAG AAG ATT GTA AAC CGG GAT GTG AAA 1047 Pro Pro Ser Lys Ser His His Lys Lys Ile Val Asn Arg Asp Val Lys 250 255 260 CCC TTT CCT GGG ACT GTG GCG AAG ATG TTT TTG AGC ACC TTG ACA ATA 1095 Pro Phe Pro Gly Thr Val Ala Lys Met Phe Leu Ser Thr Leu Thr Ile 265 270 275 GAA AGT GTG ACC AAG AGT GAC CAA GGG GAA TAC ACC TGT GTA GCG TCC 1143 Glu Ser Val Thr Lys Ser Asp Gln Gly Glu Tyr Thr Cys Val Ala Ser 280 285 290 AGT GGA CGG ATG ATC AAG AGA AAT AGA ACA TTT GTC CGA GTT CAC ACA 1191 Ser Gly Arg Met Ile Lys Arg Asn Arg Thr Phe Val Arg Val His Thr 295 300 305 AAG CCT TTT ATT GCT TTC GGT AGT GGG ATG AAA TCT TTG GTG GAA GCC 1239 Lys Pro Phe Ile Ala Phe Gly Ser Gly Met Lys Ser Leu Val Glu Ala 310 315 320 325 ACA GTG GGC AGT CAA GTC CGA ATC CCT GTG AAG TAT CTC AGT TAC CCA 1287 Thr Val Gly Ser Gln Val Arg Ile Pro Val Lys Tyr Leu Ser Tyr Pro 330 335 340 GCT CCT GAT ATC AAA TGG TAC AGA AAT GGA AGG CCC ATT GAG TCC AAC 1335 Ala Pro Asp Ile Lys Trp Tyr Arg Asn Gly Arg Pro Ile Glu Ser Asn 345 350 355 TAC ACA ATG ATT GTT GGC GAT GAA CTC ACC ATC ATG GAA GTG ACT GAA 1383 Tyr Thr Met Ile Val Gly Asp Glu Leu Thr Ile Met Glu Val Thr Glu 360 365 370 AGA GAT GCA GGA AAC TAC ACG GTC ATC CTC ACC AAC CCC ATT TCA ATG 1431 Arg Asp Ala Gly Asn Tyr Thr Val Ile Leu Thr Asn Pro Ile Ser Met 375 380 385 GAG AAA CAG AGC CAC ATG GTC TCT CTG GTT GTG AAT GTC CCA CCC CAG 1479 Glu Lys Gln Ser His Met Val Ser Leu Val Val Asn Val Pro Pro Gln 390 395 400 405 ATC GGT GAG AAA GCC TTG ATC TCG CCT ATG GAT TCC TAC CAG TAT GGG 1527 Ile Gly Glu Lys Ala Leu Ile Ser Pro Met Asp Ser Tyr Gln Tyr Gly 410 415 420 ACC ATG CAG ACA TTG ACA TGC ACA GTC TAC GCC AAC CCT CCC CTG CAC 1575 Thr Met Gln Thr Leu Thr Cys Thr Val Tyr Ala Asn Pro Pro Leu His 425 430 435 CAC ATC CAG TGG TAC TGG CAG CTA GAA GAA GCC TGC TCC TAC AGA CCC 1623 His Ile Gln Trp Tyr Trp Gln Leu Glu Glu Ala Cys Ser Tyr Arg Pro 440 445 450 GGC CAA ACA AGC CCG TAT GCT TGT AAA GAA TGG AGA CAC GTG GAG GAT 1671 Gly Gln Thr Ser Pro Tyr Ala Cys Lys Glu Trp Arg His Val Glu Asp 455 460 465 TTC CAG GGG GGA AAC AAG ATC GAA GTC ACC AAA AAC CAA TAT GCC CTG 1719 Phe Gln Gly Gly Asn Lys Ile Glu Val Thr Lys Asn Gln Tyr Ala Leu 470 475 480 485 ATT GAA GGA AAA AAC AAA ACT GTA AGT ACG CTG GTC ATC CAA GCT GCC 1767 Ile Glu Gly Lys Asn Lys Thr Val Ser Thr Leu Val Ile Gln Ala Ala 490 495 500 AAC GTG TCA GCG TTG TAC AAA TGT GAA GCC ATC AAC AAA GCG GGA CGA 1815 Asn Val Ser Ala Leu Tyr Lys Cys Glu Ala Ile Asn Lys Ala Gly Arg 505 510 515 GGA GAG AGG GTC ATC TCC TTC CAT GTG ATC AGG GGT CCT GAA ATT ACT 1863 Gly Glu Arg Val Ile Ser Phe His Val Ile Arg Gly Pro Glu Ile Thr 520 525 530 GTG CAA CCT GCT GCC CAG CCA ACT GAG CAG GAG AGT GTG TCC CTG TTG 1911 Val Gln Pro Ala Ala Gln Pro Thr Glu Gln Glu Ser Val Ser Leu Leu 535 540 545 TGC ACT GCA GAC AGA AAT ACG TTT GAG AAC CTC ACG TGG TAC AAG CTT 1959 Cys Thr Ala Asp Arg Asn Thr Phe Glu Asn Leu Thr Trp Tyr Lys Leu 550 555 560 565 GGC TCA CAG GCA ACA TCG GTC CAC ATG GGC GAA TCA CTC ACA CCA GTT 2007 Gly Ser Gln Ala Thr Ser Val His Met Gly Glu Ser Leu Thr Pro Val 570 575 580 TGC AAG AAC TTG GAT GCT CTT TGG AAA CTG AAT GGC ACC ATG TTT TCT 2055 Cys Lys Asn Leu Asp Ala Leu Trp Lys Leu Asn Gly Thr Met Phe Ser 585 590 595 AAC AGC ACA AAT GAC ATC TTG ATT GTG GCA TTT CAG AAT GCC TCT CTG 2103 Asn Ser Thr Asn Asp Ile Leu Ile Val Ala Phe Gln Asn Ala Ser Leu 600 605 610 CAG GAC CAA GGC GAC TAT GTT TGC TCT GCT CAA GAT AAG AAG ACC AAG 2151 Gln Asp Gln Gly Asp Tyr Val Cys Ser Ala Gln Asp Lys Lys Thr Lys 615 620 625 AAA AGA CAT TGC CTG GTC AAA CAG CTC ATC ATC CTA GAG CGC ATG GCA 2199 Lys Arg His Cys Leu Val Lys Gln Leu Ile Ile Leu Glu Arg Met Ala 630 635 640 645 CCC ATG ATC ACC GGA AAT CTG GAG AAT CAG ACA ACA ACC ATT GGC GAG 2247 Pro Met Ile Thr Gly Asn Leu Glu Asn Gln Thr Thr Thr Ile Gly Glu 650 655 660 ACC ATT GAA GTG ACT TGC CCA GCA TCT GGA AAT CCT ACC CCA CAC ATT 2295 Thr Ile Glu Val Thr Cys Pro Ala Ser Gly Asn Pro Thr Pro His Ile 665 670 675 ACA TGG TTC AAA GAC AAC GAG ACC CTG GTA GAA GAT TCA GGC ATT GTA 2343 Thr Trp Phe Lys Asp Asn Glu Thr Leu Val Glu Asp Ser Gly Ile Val 680 685 690 CTG AGA GAT GGG AAC CGG AAC CTG ACT ATC CGC AGG GTG AGG AAG GAG 2391 Leu Arg Asp Gly Asn Arg Asn Leu Thr Ile Arg Arg Val Arg Lys Glu 695 700 705 GAT GGA GGC CTC TAC ACC TGC CAG GCC TGC AAT GTC CTT GGC TGT GCA 2439 Asp Gly Gly Leu Tyr Thr Cys Gln Ala Cys Asn Val Leu Gly Cys Ala 710 715 720 725 AGA GCG GAG ACG CTC TTC ATA ATA GAA GGT GCC CAG GAA AAG ACC AAC 2487 Arg Ala Glu Thr Leu Phe Ile Ile Glu Gly Ala Gln Glu Lys Thr Asn 730 735 740 TTG GAA GTC ATT ATC CTC GTC GGC ACT GCA GTG ATT GCC ATG TTC TTC 2535 Leu Glu Val Ile Ile Leu Val Gly Thr Ala Val Ile Ala Met Phe Phe 745 750 755 TGG CTC CTT CTT GTC ATT CTC GTA CGG ACC GTT AAG CGG GCC AAT GAA 2583 Trp Leu Leu Leu Val Ile Leu Val Arg Thr Val Lys Arg Ala Asn Glu 760 765 770 GGG GAA CTG AAG ACA GGC TAC TTG TCT ATT GTC ATG GAT CCA GAT GAA 2631 Gly Glu Leu Lys Thr Gly Tyr Leu Ser Ile Val Met Asp Pro Asp Glu 775 780 785 TTG CCC TTG GAT GAG CGC TGT GAA CGC TTG CCT TAT GAT GCC AGC AAG 2679 Leu Pro Leu Asp Glu Arg Cys Glu Arg Leu Pro Tyr Asp Ala Ser Lys 790 795 800 805 TGG GAA TTC CCC AGG GAC CGG CTG AAA CTA GGA AAA CCT CTT GGC CGC 2727 Trp Glu Phe Pro Arg Asp Arg Leu Lys Leu Gly Lys Pro Leu Gly Arg 810 815 820 GGT GCC TTC GGC CAA GTG ATT GAG GCA GAC GCT TTT GGA ATT GAC AAG 2775 Gly Ala Phe Gly Gln Val Ile Glu Ala Asp Ala Phe Gly Ile Asp Lys 825 830 835 ACA GCG ACT TGC AAA ACA GTA GCC GTC AAG ATG TTG AAA GAA GGA GCA 2823 Thr Ala Thr Cys Lys Thr Val Ala Val Lys Met Leu Lys Glu Gly Ala 840 845 850 ACA CAC AGC GAG CAT CGA GCC CTC ATG TCT GAA CTC AAG ATC CTC ATC 2871 Thr His Ser Glu His Arg Ala Leu Met Ser Glu Leu Lys Ile Leu Ile 855 860 865 CAC ATT GGT CAC CAT CTC AAT GTG GTG AAC CTC CTA GGC GCC TGC ACC 2919 His Ile Gly His His Leu Asn Val Val Asn Leu Leu Gly Ala Cys Thr 870 875 880 885 AAG CCG GGA GGG CCT CTC ATG GTG ATT GTG GAA TTC TCG AAG TTT GGA 2967 Lys Pro Gly Gly Pro Leu Met Val Ile Val Glu Phe Ser Lys Phe Gly 890 895 900 AAC CTA TCA ACT TAC TTA CGG GGC AAG AGA AAT GAA TTT GTT CCC TAT 3015 Asn Leu Ser Thr Tyr Leu Arg Gly Lys Arg Asn Glu Phe Val Pro Tyr 905 910 915 AAG AGC AAA GGG GCA CGC TTC CGC CAG GGC AAG GAC TAC GTT GGG GAG 3063 Lys Ser Lys Gly Ala Arg Phe Arg Gln Gly Lys Asp Tyr Val Gly Glu 920 925 930 CTC TCC GTG GAT CTG AAA AGA CGC TTG GAC AGC ATC ACC AGC AGC CAG 3111 Leu Ser Val Asp Leu Lys Arg Arg Leu Asp Ser Ile Thr Ser Ser Gln 935 940 945 AGC TCT GCC AGC TCA GGC TTT GTT GAG GAG AAA TCG CTC AGT GAT GTA 3159 Ser Ser Ala Ser Ser Gly Phe Val Glu Glu Lys Ser Leu Ser Asp Val 950 955 960 965 GAG GAA GAA GAA GCT TCT GAA GAA CTG TAC AAG GAC TTC CTG ACC TTG 3207 Glu Glu Glu Glu Ala Ser Glu Glu Leu Tyr Lys Asp Phe Leu Thr Leu 970 975 980 GAG CAT CTC ATC TGT TAC AGC TTC CAA GTG GCT AAG GGC ATG GAG TTC 3255 Glu His Leu Ile Cys Tyr Ser Phe Gln Val Ala Lys Gly Met Glu Phe 985 990 995 TTG GCA TCA AGG AAG TGT ATC CAC AGG GAC CTG GCA GCA CGA AAC ATT 3303 Leu Ala Ser Arg Lys Cys Ile His Arg Asp Leu Ala Ala Arg Asn Ile 1000 1005 1010 CTC CTA TCG GAG AAG AAT GTG GTT AAG ATC TGT GAC TTC GGC TTG GCC 3351 Leu Leu Ser Glu Lys Asn Val Val Lys Ile Cys Asp Phe Gly Leu Ala 1015 1020 1025 CGG GAC ATT TAT AAA GAC CCG GAT TAT GTC AGA AAA GGA GAT GCC CGA 3399 Arg Asp Ile Tyr Lys Asp Pro Asp Tyr Val Arg Lys Gly Asp Ala Arg 1030 1035 1040 1045 CTC CCT TTG AAG TGG ATG GCC CCG GAA ACC ATT TTT GAC AGA GTA TAC 3447 Leu Pro Leu Lys Trp Met Ala Pro Glu Thr Ile Phe Asp Arg Val Tyr 1050 1055 1060 ACA ATT CAG AGC GAT GTG TGG TCT TTC GGT GTG TTG CTC TGG GAA ATA 3495 Thr Ile Gln Ser Asp Val Trp Ser Phe Gly Val Leu Leu Trp Glu Ile 1065 1070 1075 TTT TCC TTA GGT GCC TCC CCA TAC CCT GGG GTC AAG ATT GAT GAA GAA 3543 Phe Ser Leu Gly Ala Ser Pro Tyr Pro Gly Val Lys Ile Asp Glu Glu 1080 1085 1090 TTT TGT AGG AGA TTG AAA GAA GGA ACT AGA ATG CGG GCT CCT GAC TAC 3591 Phe Cys Arg Arg Leu Lys Glu Gly Thr Arg Met Arg Ala Pro Asp Tyr 1095 1100 1105 ACT ACC CCA GAA ATG TAC CAG ACC ATG CTG GAC TGC TGG CAT GAG GAC 3639 Thr Thr Pro Glu Met Tyr Gln Thr Met Leu Asp Cys Trp His Glu Asp 1110 1115 1120 1125 CCC AAC CAG AGA CCC TCG TTT TCA GAG TTG GTG GAG CAT TTG GGA AAC 3687 Pro Asn Gln Arg Pro Ser Phe Ser Glu Leu Val Glu His Leu Gly Asn 1130 1135 1140 CTC CTG CAA GCA AAT GCG CAG CAG GAT GGC AAA GAC TAT ATT GTT CTT 3735 Leu Leu Gln Ala Asn Ala Gln Gln Asp Gly Lys Asp Tyr Ile Val Leu 1145 1150 1155 CCA ATG TCA GAG ACA CTG AGC ATG GAA GAG GAT TCT GGA CTC TCC CTG 3783 Pro Met Ser Glu Thr Leu Ser Met Glu Glu Asp Ser Gly Leu Ser Leu 1160 1165 1170 CCT ACC TCA CCT GTT TCC TGT ATG GAG GAA GAG GAA GTG TGC GAC CCC 3831 Pro Thr Ser Pro Val Ser Cys Met Glu Glu Glu Glu Val Cys Asp Pro 1175 1180 1185 AAA TTC CAT TAT GAC AAC ACA GCA GGA ATC AGT CAT TAT CTC CAG AAC 3879 Lys Phe His Tyr Asp Asn Thr Ala Gly Ile Ser His Tyr Leu Gln Asn 1190 1195 1200 1205 AGT AAG CGA AAG AGC CGG CCA GTG AGT GTA AAA ACA TTT GAA GAT ATC 3927 Ser Lys Arg Lys Ser Arg Pro Val Ser Val Lys Thr Phe Glu Asp Ile 1210 1215 1220 CCA TTG GAG GAA CCA GAA GTA AAA GTG ATC CCA GAT GAC AGC CAG ACA 3975 Pro Leu Glu Glu Pro Glu Val Lys Val Ile Pro Asp Asp Ser Gln Thr 1225 1230 1235 GAC AGT GGG ATG GTC CTT GCA TCA GAA GAG CTG AAA ACT CTG GAA GAC 4023 Asp Ser Gly Met Val Leu Ala Ser Glu Glu Leu Lys Thr Leu Glu Asp 1240 1245 1250 AGG AAC AAA TTA TCT CCA TCT TTT GGT GGA ATG ATG CCC AGT AAA AGC 4071 Arg Asn Lys Leu Ser Pro Ser Phe Gly Gly Met Met Pro Ser Lys Ser 1255 1260 1265 AGG GAG TCT GTG GCC TCG GAA GGC TCC AAC CAG ACC AGT GGC TAC CAG 4119 Arg Glu Ser Val Ala Ser Glu Gly Ser Asn Gln Thr Ser Gly Tyr Gln 1270 1275 1280 1285 TCT GGG TAT CAC TCA GAT GAC ACA GAC ACC ACC GTG TAC TCC AGC GAC 4167 Ser Gly Tyr His Ser Asp Asp Thr Asp Thr Thr Val Tyr Ser Ser Asp 1290 1295 1300 GAG GCA GGA CTT TTA AAG ATG GTG GAT GCT GCA GTT CAC GCT GAC TCA 4215 Glu Ala Gly Leu Leu Lys Met Val Asp Ala Ala Val His Ala Asp Ser 1305 1310 1315 GGG ACC ACA CTG CAG CTC ACC TCC TGT TTA AAT GGA AGT GGT CCT GTC 4263 Gly Thr Thr Leu Gln Leu Thr Ser Cys Leu Asn Gly Ser Gly Pro Val 1320 1325 1330 CCG GCT CCG CCC CCA ACT CCT GGA AAT CAC GAG AGA GGT GCT GCT TAG 4318 Pro Ala Pro Pro Pro Thr Pro Gly Asn His Glu Arg Gly Ala Ala 1335 1340 1345 AGTGTTGTTC TTTCCACCAC CCGGAAGTAG CCACATTTGA TTTTCATTTT TGGAGGAG 4378 ACCTCAGACT GCAAGGAGCT TGTCCTCAGG GCATTTCCAG AGAAGATGCC CATGACCC 4438 GAATGTGTTG ACTCTACTCT CTTTTCCATT CATTTAAAAG TCCTATATAA TGTGCCCT 4498 TGTGGTCTCA CTACCAGTTA AAGCAAAAGA CTTTCAAACA CGTGGACTCT GTCCTCCA 4558 AAGTGGCAAC GGCACCTCTG TGAAACTGGA TCGAATGGGC AATGCTTTGT GTGTTGAG 4618 TGGGTGAGAT GTCCCAGGGC CGAGTCTGTC TACCTTGGAG GCTTTGTGGA GGATGCGG 4678 ATGAGCCAAG TGTTAAGTGT GGGATGTGGA CTGGGAGGAA GGAAGGCGCA AGCCGTCC 4738 AGAGCGGTTG GAGCCTGCAG ATGCATTGTG CTGGCTCTGG TGGAGGTGGG CTTGTGGC 4798 GTCAGGAAAC GCAAAGGCGG CCGGCAGGGT TTGGTTTTGG AAGGTTTGCG TGCTCTTC 4858 AGTCGGGTTA CAGGCGAGTT CCCTGTGGCG TTTCCTACTC CTAATGAGAG TTCCTTCC 4918 ACTCTTACGT GTCTCCTGGC CTGGCCCCAG GAAGGAAATG ATGCAGCTTG CTCCTTCC 4978 ATCTCTCAGG CTGTGCCTTA ATTCAGAACA CCAAAAGAGA GGAACGTCGG CAGAGGCT 5038 TGACGGGGCC GAAGAATTGT GAGAACAGAA CAGAAACTCA GGGTTTCTGC TGGGTGGA 5098 CCCACGTGGC GCCCTGGTGG CAGGTCTGAG GGTTCTCTGT CAAGTGGCGG TAAAGGCT 5158 GGCTGGTGTT CTTCCTCTAT CTCCACTCCT GTCAGGCCCC CAAGTCCTCA GTATTTTA 5218 TTTGTGGCTT CCTGATGGCA GAAAAATCTT AATTGGTTGG TTTGCTCTCC AGATAATC 5278 TAGCCAGATT TCGAAATTAC TTTTTAGCCG AGGTTATGAT AACATCTACT GTATCCTT 5338 GAATTTTAAC CTATAAAACT ATGTCTACTG GTTTCTGCCT GTGTGCTTAT GTTAAAAA 5398 AAAAAAAA 5406 1367 amino acids amino acid linear protein 6 Met Glu Ser Lys Gly Leu Leu Ala Val Ala Leu Trp Phe Cys Val Glu -19 -15 -10 -5 Thr Arg Ala Ala Ser Val Gly Leu Pro Gly Asp Phe Leu His Pro Pro 1 5 10 Lys Leu Ser Thr Gln Lys Asp Ile Leu Thr Ile Leu Ala Asn Thr Thr 15 20 25 Leu Gln Ile Thr Cys Arg Gly Gln Arg Asp Leu Asp Trp Leu Trp Pro 30 35 40 45 Asn Ala Gln Arg Asp Ser Glu Glu Arg Val Leu Val Thr Glu Cys Gly 50 55 60 Gly Gly Asp Ser Ile Phe Cys Lys Thr Leu Thr Ile Pro Arg Val Val 65 70 75 Gly Asn Asp Thr Gly Ala Tyr Lys Cys Ser Tyr Arg Asp Val Asp Ile 80 85 90 Ala Ser Thr Val Tyr Val Tyr Val Arg Asp Tyr Arg Ser Pro Phe Ile 95 100 105 Ala Ser Val Ser Asp Gln His Gly Ile Val Tyr Ile Thr Glu Asn Lys 110 115 120 125 Asn Lys Thr Val Val Ile Pro Cys Arg Gly Ser Ile Ser Asn Leu Asn 130 135 140 Val Ser Leu Cys Ala Arg Tyr Pro Glu Lys Arg Phe Val Pro Asp Gly 145 150 155 Asn Arg Ile Ser Trp Asp Ser Glu Ile Gly Phe Thr Leu Pro Ser Tyr 160 165 170 Met Ile Ser Tyr Ala Gly Met Val Phe Cys Glu Ala Lys Ile Asn Asp 175 180 185 Glu Thr Tyr Gln Ser Ile Met Tyr Ile Val Val Val Val Gly Tyr Arg 190 195 200 205 Ile Tyr Asp Val Ile Leu Ser Pro Pro His Glu Ile Glu Leu Ser Ala 210 215 220 Gly Glu Lys Leu Val Leu Asn Cys Thr Ala Arg Thr Glu Leu Asn Val 225 230 235 Gly Leu Asp Phe Thr Trp His Ser Pro Pro Ser Lys Ser His His Lys 240 245 250 Lys Ile Val Asn Arg Asp Val Lys Pro Phe Pro Gly Thr Val Ala Lys 255 260 265 Met Phe Leu Ser Thr Leu Thr Ile Glu Ser Val Thr Lys Ser Asp Gln 270 275 280 285 Gly Glu Tyr Thr Cys Val Ala Ser Ser Gly Arg Met Ile Lys Arg Asn 290 295 300 Arg Thr Phe Val Arg Val His Thr Lys Pro Phe Ile Ala Phe Gly Ser 305 310 315 Gly Met Lys Ser Leu Val Glu Ala Thr Val Gly Ser Gln Val Arg Ile 320 325 330 Pro Val Lys Tyr Leu Ser Tyr Pro Ala Pro Asp Ile Lys Trp Tyr Arg 335 340 345 Asn Gly Arg Pro Ile Glu Ser Asn Tyr Thr Met Ile Val Gly Asp Glu 350 355 360 365 Leu Thr Ile Met Glu Val Thr Glu Arg Asp Ala Gly Asn Tyr Thr Val 370 375 380 Ile Leu Thr Asn Pro Ile Ser Met Glu Lys Gln Ser His Met Val Ser 385 390 395 Leu Val Val Asn Val Pro Pro Gln Ile Gly Glu Lys Ala Leu Ile Ser 400 405 410 Pro Met Asp Ser Tyr Gln Tyr Gly Thr Met Gln Thr Leu Thr Cys Thr 415 420 425 Val Tyr Ala Asn Pro Pro Leu His His Ile Gln Trp Tyr Trp Gln Leu 430 435 440 445 Glu Glu Ala Cys Ser Tyr Arg Pro Gly Gln Thr Ser Pro Tyr Ala Cys 450 455 460 Lys Glu Trp Arg His Val Glu Asp Phe Gln Gly Gly Asn Lys Ile Glu 465 470 475 Val Thr Lys Asn Gln Tyr Ala Leu Ile Glu Gly Lys Asn Lys Thr Val 480 485 490 Ser Thr Leu Val Ile Gln Ala Ala Asn Val Ser Ala Leu Tyr Lys Cys 495 500 505 Glu Ala Ile Asn Lys Ala Gly Arg Gly Glu Arg Val Ile Ser Phe His 510 515 520 525 Val Ile Arg Gly Pro Glu Ile Thr Val Gln Pro Ala Ala Gln Pro Thr 530 535 540 Glu Gln Glu Ser Val Ser Leu Leu Cys Thr Ala Asp Arg Asn Thr Phe 545 550 555 Glu Asn Leu Thr Trp Tyr Lys Leu Gly Ser Gln Ala Thr Ser Val His 560 565 570 Met Gly Glu Ser Leu Thr Pro Val Cys Lys Asn Leu Asp Ala Leu Trp 575 580 585 Lys Leu Asn Gly Thr Met Phe Ser Asn Ser Thr Asn Asp Ile Leu Ile 590 595 600 605 Val Ala Phe Gln Asn Ala Ser Leu Gln Asp Gln Gly Asp Tyr Val Cys 610 615 620 Ser Ala Gln Asp Lys Lys Thr Lys Lys Arg His Cys Leu Val Lys Gln 625 630 635 Leu Ile Ile Leu Glu Arg Met Ala Pro Met Ile Thr Gly Asn Leu Glu 640 645 650 Asn Gln Thr Thr Thr Ile Gly Glu Thr Ile Glu Val Thr Cys Pro Ala 655 660 665 Ser Gly Asn Pro Thr Pro His Ile Thr Trp Phe Lys Asp Asn Glu Thr 670 675 680 685 Leu Val Glu Asp Ser Gly Ile Val Leu Arg Asp Gly Asn Arg Asn Leu 690 695 700 Thr Ile Arg Arg Val Arg Lys Glu Asp Gly Gly Leu Tyr Thr Cys Gln 705 710 715 Ala Cys Asn Val Leu Gly Cys Ala Arg Ala Glu Thr Leu Phe Ile Ile 720 725 730 Glu Gly Ala Gln Glu Lys Thr Asn Leu Glu Val Ile Ile Leu Val Gly 735 740 745 Thr Ala Val Ile Ala Met Phe Phe Trp Leu Leu Leu Val Ile Leu Val 750 755 760 765 Arg Thr Val Lys Arg Ala Asn Glu Gly Glu Leu Lys Thr Gly Tyr Leu 770 775 780 Ser Ile Val Met Asp Pro Asp Glu Leu Pro Leu Asp Glu Arg Cys Glu 785 790 795 Arg Leu Pro Tyr Asp Ala Ser Lys Trp Glu Phe Pro Arg Asp Arg Leu 800 805 810 Lys Leu Gly Lys Pro Leu Gly Arg Gly Ala Phe Gly Gln Val Ile Glu 815 820 825 Ala Asp Ala Phe Gly Ile Asp Lys Thr Ala Thr Cys Lys Thr Val Ala 830 835 840 845 Val Lys Met Leu Lys Glu Gly Ala Thr His Ser Glu His Arg Ala Leu 850 855 860 Met Ser Glu Leu Lys Ile Leu Ile His Ile Gly His His Leu Asn Val 865 870 875 Val Asn Leu Leu Gly Ala Cys Thr Lys Pro Gly Gly Pro Leu Met Val 880 885 890 Ile Val Glu Phe Ser Lys Phe Gly Asn Leu Ser Thr Tyr Leu Arg Gly 895 900 905 Lys Arg Asn Glu Phe Val Pro Tyr Lys Ser Lys Gly Ala Arg Phe Arg 910 915 920 925 Gln Gly Lys Asp Tyr Val Gly Glu Leu Ser Val Asp Leu Lys Arg Arg 930 935 940 Leu Asp Ser Ile Thr Ser Ser Gln Ser Ser Ala Ser Ser Gly Phe Val 945 950 955 Glu Glu Lys Ser Leu Ser Asp Val Glu Glu Glu Glu Ala Ser Glu Glu 960 965 970 Leu Tyr Lys Asp Phe Leu Thr Leu Glu His Leu Ile Cys Tyr Ser Phe 975 980 985 Gln Val Ala Lys Gly Met Glu Phe Leu Ala Ser Arg Lys Cys Ile His 990 995 1000 1005 Arg Asp Leu Ala Ala Arg Asn Ile Leu Leu Ser Glu Lys Asn Val Val 1010 1015 1020 Lys Ile Cys Asp Phe Gly Leu Ala Arg Asp Ile Tyr Lys Asp Pro Asp 1025 1030 1035 Tyr Val Arg Lys Gly Asp Ala Arg Leu Pro Leu Lys Trp Met Ala Pro 1040 1045 1050 Glu Thr Ile Phe Asp Arg Val Tyr Thr Ile Gln Ser Asp Val Trp Ser 1055 1060 1065 Phe Gly Val Leu Leu Trp Glu Ile Phe Ser Leu Gly Ala Ser Pro Tyr 1070 1075 1080 1085 Pro Gly Val Lys Ile Asp Glu Glu Phe Cys Arg Arg Leu Lys Glu Gly 1090 1095 1100 Thr Arg Met Arg Ala Pro Asp Tyr Thr Thr Pro Glu Met Tyr Gln Thr 1105 1110 1115 Met Leu Asp Cys Trp His Glu Asp Pro Asn Gln Arg Pro Ser Phe Ser 1120 1125 1130 Glu Leu Val Glu His Leu Gly Asn Leu Leu Gln Ala Asn Ala Gln Gln 1135 1140 1145 Asp Gly Lys Asp Tyr Ile Val Leu Pro Met Ser Glu Thr Leu Ser Met 1150 1155 1160 1165 Glu Glu Asp Ser Gly Leu Ser Leu Pro Thr Ser Pro Val Ser Cys Met 1170 1175 1180 Glu Glu Glu Glu Val Cys Asp Pro Lys Phe His Tyr Asp Asn Thr Ala 1185 1190 1195 Gly Ile Ser His Tyr Leu Gln Asn Ser Lys Arg Lys Ser Arg Pro Val 1200 1205 1210 Ser Val Lys Thr Phe Glu Asp Ile Pro Leu Glu Glu Pro Glu Val Lys 1215 1220 1225 Val Ile Pro Asp Asp Ser Gln Thr Asp Ser Gly Met Val Leu Ala Ser 1230 1235 1240 1245 Glu Glu Leu Lys Thr Leu Glu Asp Arg Asn Lys Leu Ser Pro Ser Phe 1250 1255 1260 Gly Gly Met Met Pro Ser Lys Ser Arg Glu Ser Val Ala Ser Glu Gly 1265 1270 1275 Ser Asn Gln Thr Ser Gly Tyr Gln Ser Gly Tyr His Ser Asp Asp Thr 1280 1285 1290 Asp Thr Thr Val Tyr Ser Ser Asp Glu Ala Gly Leu Leu Lys Met Val 1295 1300 1305 Asp Ala Ala Val His Ala Asp Ser Gly Thr Thr Leu Gln Leu Thr Ser 1310 1315 1320 1325 Cys Leu Asn Gly Ser Gly Pro Val Pro Ala Pro Pro Pro Thr Pro Gly 1330 1335 1340 Asn His Glu Arg Gly Ala Ala 1345 96 base pairs nucleic acid single linear cDNA NO NO 7 AATTCGTCGA CTTTCTGTCA CCATGAGTGC ACTTCTGATC CTAGCCCTTG TGGGAGCTGC 60 TGTTGCTGAC TACAAAGATG ATGATGACAA GATCTA 96 96 base pairs nucleic acid single linear cDNA NO NO 8 AGCTTAGATC TTGTCATCAT CATCTTTGTA GTCAGCAACA GCAGCTCCCA CAGAGGCTAG 60 GATCAGAAGT GCACTCATGG TGACAGAAAG TCGACG 96 30 base pairs nucleic acid single linear cDNA NO NO 9 TGAGAAGATC TCAAACCAAG ACCTGCCTGT 30 34 base pairs nucleic acid single linear cDNA NO NO 10 CCAATGGCGG CCGCTCAGGA GATGTTGTCT TGGA 34 

What I claim is:
 1. An isolated mammalian nucleic acid molecule encoding a receptor protein tyrosine kinase expressed in primitive hematopoietic cells and not expressed in mature hematopoietic cells.
 2. A nucleic acid molecule according to claim 1 wherein the nucleic acid molecule is DNA.
 3. A nucleic acid molecule according to claim 2 wherein the nucleic acid molecule is cDNA.
 4. A nucleic acid molecule according to claim 1 wherein the nucleic acid molecule is RNA.
 5. A nucleic acid molecule according to claim 1 that is a mouse nucleic acid molecule.
 6. A nucleic acid molecule according to claim 5 that is flk-2 comprising the sequence shown in FIG. 1a and SEQ. ID. NO.
 1. 7. A nucleic acid molecule according to claim 1 that is a human nucleic acid molecule.
 8. A nucleic acid molecule according to claim 7 that is DNA.
 9. A nucleic acid molecule according to claim 7 that is flk-2 comprising the sequence shown in FIG. 1b and SEQ. ID. NO.
 3. 10. An isolated acid nucleic molecule that is flk-2 comprising the sequence shown in FIG. 1a and SEQ. ID. NO.
 1. 11. A nucleic acid molecule according to claim 10 wherein the nucleic acid molecule is DNA.
 12. An isolated nucleic acid molecule that is flk-2 comprising the sequence shown in FIG. 1b and SEQ. ID. NO.
 3. 13. A nucleic acid molecule according to claim 12 wherein the nucleic acid molecule is DNA.
 14. An isolated nucleic molecule that is flk-1 having the sequence shown in FIG. 2 and SEQ. ID. NO.
 5. 15. A nucleic acid molecule according to claim 14 wherein the nucleic acid molecule is DNA.
 16. A nucleic acid molecule according to claim 14 wherein the nucleic acid molecule is cDNA.
 17. A nucleic acid molecule according to claim 14 that has the corresponding sequence of RNA.
 18. A vector comprising a mammalian nucleic acid molecule encoding a receptor protein tyrosine kinase expressed in primitive hematopoietic cells and not expressed in mature hematopoietic cells.
 19. A vector comprising flk-1 having the nucleic acid sequence of FIG. 2 and SEQ. ID. NO.
 5. 20. A vector comprising flk-2 having the nucleic acid sequence of FIG. 1a and SEQ. ID. NO. 1 or FIG. 1b and SEQ. ID. NO.
 3. 21. A vector according to claim 18 wherein the vector is capable of being cloned in a host.
 22. A vector according to claim 19 wherein the vector is capable of being cloned in a host.
 23. A vector according to claim 20 wherein the vector is capable of being cloned in a host.
 24. A vector according to claim 21 wherein the host is a prokaryotic host.
 25. A vector according to claim 22 wherein the host is a prokaryotic host.
 26. A vector according to claim 23 wherein the host is a prokaryotic host.
 27. A vector according to claim 18 that is capable of expressing the nucleic acid molecule in a host.
 28. A vector according to claim 19 that is capable of expressing flk-1 in a host.
 29. A vector according to claim 20 that is capable of expressing flk-2 in a host.
 30. A vector according to claim 27 wherein the host is a prokaryotic host.
 31. A vector according to claim 28 wherein the host is a prokaryotic host.
 32. A vector according to claim 29 wherein the host is a prokaryotic host.
 33. A vector according to claim 27 wherein the host is a eucaryotic host.
 34. A vector according to claim 28 wherein the host is a eucaryotic host.
 35. A vector according to claim 29 wherein the host is a eucaryotic host.
 36. An isolated protein tyrosine kinase expressed in primitive hematopoietic cells and not expressed in mature hematopoietic cells.
 37. The protein tyrosine kinase according to claim 36 that is flk-2 having the sequence shown in FIG. 1a and SEQ. ID. NO. 1 or FIG. 1b and SEQ. ID. NO.
 3. 38. The protein tyrosine kinase according to claim 36 that is human flk-2.
 39. The protein tyrosine kinase according to claim 38 that is flk-2 having the sequence shown in FIG. 1b and SEQ. ID. NO.
 3. 40. An isolated protein tyrosine kinase that is flk-1 having the sequence shown in FIG. 2 and SEQ. ID. NO.
 5. 41. A ligand that binds to a receptor protein tyrosine kinase expressed in primitive mammalian hematopoietic cells and not expressed in mature hematopoietic cells, wherein the ligand stimulates the proliferation and/or differentiation of the primitive hematopoietic cells.
 42. A ligand that binds to the receptor protein tyrosine kinase having the amino acid sequence of flk-1 shown in FIG. 2 and SEQ. ID. NO. 5, wherein the ligand stimulates the proliferation and/or differentiation of cells that express flk-1.
 43. A ligand that binds to the receptor protein tyrosine kinase having the amino acid sequence of flk-2 shown in FIG. 1a and SEQ. ID. NO. 1 or FIG. 1b and SEQ. ID. NO. 3, wherein the ligand stimulates the proliferation and/or differentiation of cells that express flk-2.
 44. A nucleic acid molecule encoding a ligand that binds to a receptor protein tyrosine kinase expressed in primitive mammalian hematopoietic cells and not expressed in mature hematopoietic cells, wherein the ligand stimulates the proliferation and/or differentiation of the primitive hematopoietic cells.
 45. A nucleic acid molecule encoding a ligand that binds to the receptor protein tyrosine kinase having the amino acid sequence of flk-1 shown in FIG. 2 and SEQ. ID. NO. 5, wherein the ligand stimulates the proliferation and/or differentiation of cells that express flk-1.
 46. A nucleic acid molecule encoding a ligand that binds to the receptor protein tyrosine kinase having the amino acid sequence of flk-2 shown in FIG. 1a and SEQ. ID. NO. 1 or FIG. 1b and SEQ. ID. NO. 3, wherein the ligand stimulates the proliferation and/or differentiation of cells that express flk-2.
 47. A nucleic acid molecule according to claim 44 wherein the nucleic acid molecule is DNA.
 48. A nucleic acid molecule according to claim 44 wherein the nucleic acid molecule is cDNA.
 49. A nucleic acid molecule according to claim 44 wherein the nucleic acid molecule is RNA.
 50. A nucleic acid molecule according to claim 45 wherein the nucleic acid molecule is DNA.
 51. A nucleic acid molecule according to claim 45 wherein the nucleic acid molecule is cDNA.
 52. A nucleic acid molecule according to claim 45 wherein the nucleic acid molecule is RNA.
 53. A nucleic acid molecule according to claim 46 wherein the nucleic acid molecule is DNA.
 54. A nucleic acid molecule according to claim 46 wherein the nucleic acid molecule is cDNA.
 55. A nucleic acid molecule according to claim 46 wherein the nucleic acid molecule is RNA.
 56. A method of stimulating the proliferation and/or differentiation of primitive mammalian hematopoietic stem cells comprising contacting the stem cells with a ligand that binds to a receptor protein tyrosine kinase expressed in primitive mammalian hematopoietic cells and not expressed in mature hematopoietic cells.
 57. A method of stimulating the proliferation and/or differentiation of primitive mammalian hematopoietic stem cells comprising contacting the stem cells with a ligand that binds to the receptor protein tyrosine kinase having the nucleic acid sequence of flk-1 shown in FIG. 2 and SEQ. ID. NO.
 5. 58. A method of stimulating the proliferation and/or differentiation of primitive mammalian hematopoietic stem cells comprising contacting the stem cells with a ligand that binds to the receptor protein tyrosine kinase having the nucleic acid sequence of flk-2 shown in FIG. 1a and SEQ. ID. NO. 1 or FIG. 1b and SEQ. ID. NO.
 3. 59. A method according to claim 56 wherein the stimulation occurs in vitro.
 60. A method according to claim 57 wherein the stimulation occurs in vitro.
 61. A method according to claim 58 wherein the stimulation occurs in vitro.
 62. A method according to claim 56 wherein the stimulation occurs in vivo.
 63. A method according to claim 57 wherein the stimulation occurs in vivo.
 64. A method according to claim 58 wherein the stimulation occurs in vivo.
 65. Murine cell line 2018 having ATCC accession number ATCC CRL
 10907. 66. A recombinant nucleic acid molecule that is murine flk-2 having the sequence shown in FIG. 1a and SEQ. ID. NO.
 1. 67. A recombinant nucleic acid molecule comprising the sequence shown in FIG. 1a and SEQ. ID. NO. 1 from nucleotide 1 to nucleotide
 1662. 68. A recombinant nucleic acid molecule comprising the sequence shown in FIG. 1a and SEQ. ID. NO. 1 from nucleotide 31 to nucleotide
 3006. 69. A recombinant nucleic acid molecule comprising the sequence shown in FIG. 1a and SEQ. ID. NO. 1 from nucleotide 112 to nucleotide
 3006. 70. An isolated mRNA that encodes the murine flk-2 protein, said protein having the amino acid sequence shown in FIG. 1a and SEQ. ID. NO.
 1. 71. A recombinant nucleic acid molecule that is human flk-2 having the sequence shown in FIG. 1b and SEQ. ID. NO.
 3. 72. A recombinant nucleic acid molecule comprising the sequence shown in FIG. 1b and SEQ. ID. NO. 3 from nucleotide 1 to nucleotide
 1689. 73. A recombinant nucleic acid molecule comprising the sequence shown in FIG. 1b and SEQ. ID. NO. 3 from nucleotide 58 to nucleotide
 3036. 74. A recombinant nucleic acid molecule comprising the sequence shown in FIG. 1b and SEQ. ID. NO. 3 from nucleotide 139 to nucleotide
 3036. 75. An isolated mRNA that encodes the human flk-2 protein, said protein having the amino acid sequence shown in FIG. 1b and SEQ. ID. NO.
 3. 76. A recombinant nucleic acid molecule that is murine flk-1 having the sequence shown in FIG. 2 and SEQ. ID. NO.
 5. 77. A recombinant nucleic acid molecule comprising the sequence shown in FIG. 2 and SEQ. ID. NO. 5 from nucleotide 1 to nucleotide
 2493. 78. A recombinant nucleic acid molecule comprising the sequence shown in FIG. 2 and SEQ. ID. NO. 5 from nucleotide 208 to nucleotide
 4308. 79. A recombinant nucleic acid molecule comprising the sequence shown in FIG. 2 and SEQ. ID. NO. 5 from nucleotide 265 to nucleotide
 4308. 80. An isolated mRNA that encodes the murine flk-1 protein, said protein having the amino acid sequence shown in FIG. 2 and SEQ. ID. NO.
 5. 